To buy or not to buy -- that is the question every two years or so, when Adobe releases the latest and greatest version of Photoshop. There are always one or two killer features and a host of small improvements per new release that make upgrading ASAP so hard to resist.

And just like her elder sisters, Photoshop CS4 is a wicked temptress, wooing you to break out that credit card and take her home for a long, private pixel-pushing tryst. But will you still respect her in the morning? Check out our five reasons to upgrade and five reasons to pass, then download the free 30-day trial--released in mid-November--and make up your own mind.

5 Reasons to Upgrade

1: New Image Editing Options: Adobe has packed outstanding new image editing capabilities into Photoshop CS4. The one that you’re most likely to want to play with first is Content Aware Scaling, which lets you crop/resize your images vertically or horizontally without losing or distorting the most important bits. If Photoshop can’t correctly work out which parts of the image to preserve (the program tends to assume people are priority) you can easily select the correct focal points. It’s great fun, but chances are you’ll get way more use out of the less-overtly-sexy Vibrance slider, ported over from Lightroom, that lets you boost saturation for specified colors without affecting the rest of the image. It’s genius with skin tones too.  

And On-Image adjustments for Curves, Black & White, and Hue/Saturation adjustment layers lets you click inside an image and make your adjustments by dragging up and down with your mouse. The enhanced Auto-Blend Layers command lets you merge images to get the best out of a stack of similar photos (something you may have been previously painstakingly doing with masks) and the improved Dodge and Burn tools no longer seem determined to devastate your images.

2: Workspace, Sweet Workspace: Photoshop CS4 is apparently on a mission to de-clutter your screen and optimize your workflow (a dirty job but someone has to do it.) The new Application Frame corrals all of your stuff and can be easily shoved to the side of your screen or dragged over to another monitor in one fell swoop. Arrange Documents displays open files side by side, an improvement on the current Tile option. Zooming is smoother and faster at any level thanks to Photoshop’s new ability to make serious use of the power of your graphics card. Spring-loaded tools let you quickly switch to one tool and then back to the other (far more useful than you might immediately suspect), and you can now resize brushes by clicking and dragging. And each open file has its very own tab now, (like windows in your web browser) so you don’t have to dig to find the image you want.

3: Bye Palettes, Hello Panels: In a further effort to provide you with a tidy and organized screen, Photoshop CS4 features single adjustments panels rather than separate palettes. Panels first debuted in CS3, but CS4 makes better use of them, intelligently grouping image editing functions on master panels. Even cooler, you can build your own panels with the Configuration widget, adding whatever commands, content, scripts and actions your little heart desires. Photoshop CS4 comes with a useful panel that gives you access to Kuler, an Adobe community where people create and share color palettes -- a great tool for designers and anyone who sometimes struggles when conjuring up a color scheme.

4: Assorted Other Goodness: If you have a newish graphics card, Rotate Canvas lets you easily spin images in any direction by just holding down the R key and dragging -- this really simplifies drawing and finicky edits (Tablet users will love it). Color Range selection now lets you specify distance with a range slider, making it a far more useful selection tool -- no longer will it run amuck and select every instance of a color in an image. 16-bit printing is fully supported for Macs running Mac OS X 10.5+. The new Masks panel puts all masking tools up front and center, complete with vignette options. There’s a little live preview attached to the clone stamp cursor so you no longer have to retouch blindly, and Smart Objects can be linked to a layer mask. And MacBook Pro owners can use pinch to scale gestures right in Photoshop CS4 (and Bridge). 
 
5: Bridge/RAW: Camera Raw 5 gives you increased control over edits with the excellent new Adjustments Brush and Gradient Filter and now supports more than 190 camera models.. Adobe Bridge has gotten a performance boost and you can now switch from thumbnail view to a full-screen preview with one click.

5 Reasons to Not Upgrade

1: No 64-bit Support for Macs: It’s not Adobe’s fault that Photoshop CS4 for Windows supports 64-bit mode (allowing the program access to more than 3GBs of RAM) while the Mac version is still in 32-bit. Apple botched up Adobe’s plans when Carbon 64 support was pulled at the last minute. While this isn’t a total deal killer for those who aren’t regularly working with humongous files and CS4’s ability to make better use of your GPU will probably bump up image processing speed, if you don’t need CS4 features right now it might be worth waiting for the next upgrade as chances are good that 64-bit support for Mac will manifest in CS5.

2: Wait, Didn't They Just Upgrade?: CS3 was released barely 18 months ago, and while it wasn’t an OMG upgrade, there’s plenty to keep you busy and happy. So if you haven’t mastered that Vanishing Point feature yet or you’ve never worked with Smart filters, you might want to focus on exploring all of Photoshop CS3 before you upgrade.

3: Ohhh… shiny!: As you’ve noticed by now, Photoshop CS4 has plenty of super-cool features. The coolest one, Content Aware Scaling, will provide hours of fun for the whole family but seriously -- how often are you going to use it after the initial thrill fades? (Graphic designers will probably use it plenty, the rest of us, not so much). Is being able to resize a brush via dragging all that much better than hitting the bracket keys? And some of the other new features, like On-Image editing, are already available in CS3 if you have a comprehensive library of plug-ins. For example, if you use Nik Software’s filter ($249) you can already do on-image editing with amazing control of color and light (and it works in Aperture too).

4: Workflow Upgrade? Not My Workflow: Many of CS4’s improvements are workflow-related allowing you to access existing features quickly, zoom through and around your images like a speeding bullet, and customize your workspace to the max. These are all wonderful things, but depending on how you work, your skill with keyboard shortcuts, and whether you will ever bother to build custom pallets, they may not be worth the upgrade cost. So calm your new stuff craving by considering whether any of Photoshop CS4’s features will help you make more money and/or better art. If your well-reasoned answer is yes, then by all means pre-order the upgrade now.

5: Budget Issues: Sorry to bring up bad news, but we live in strange times and while the American economy relies on consumers to do their patriotic duty and shop ‘till they drop, it may be best to hang onto your bucks a little more enthusiastically than you normally would until things settle down some. Photoshop CS5 will no doubt manifest in 18-24 months and will include all of Photoshop CS4's features, as well as (probably) 64-bit support for Macs and a bunch of groovy new bits and pieces. Customers qualify for upgrade pricing from three versions back of the new release, so if you have Photoshop CS3 or CS 2 you’re not going to miss the upgrade train if you don’t buy your ticket right now.

CS4 upgrades are $199 for Photoshop CS4/ $349 for Photoshop CS4 Extended. Full (non-upgrade) versions are $699 for Photoshop CS4, $999 for Photoshop CS4 Extended.