We’ve got some good news and bad news for you: The good news is that Instapaper is coming to the iPad, possibly as early as the April 3rd in-store date! And really, we fibbed: There is no bad news.

App Store developer Marco Arment posted a preview of Instapaper for the iPad on his blog late Tuesday, complete with a host of details. First and most important, yes, Instapaper is definitely coming to iPad -- and very soon. “Possibly even on day one -- yes, I’m going for it -- but that’s optimistic,” Arment reveals.

But the best news for owners of the iPhone version of Instapaper Pro is that Arment has created a universal application that will work great on both the iPhone or the iPad. “That means that you only have to buy Instapaper Pro once to have it on both devices,” the developer says, “and the iPad edition will be available to all Pro purchases at no additional charge when it’s released.”

That’s great news for fans of the popular “save and read it later” service, which has found its way into numerous RSS feed apps in addition to the existing bookmarklet so you can save pages for later reading from any web browser.

The new version isn’t significantly different than the current one for the iPhone, with the exception of a switch to dark toolbars. “The biggest visual changes were made to the landscape-orientation list screen,” Arment writes, which can be seen in the image above. The developer has taken a nod from Apple’s Mail app for iPad and used the left side of the screen to display Instapaper folders when in horizontal mode.

“Instapaper Pro on the iPad is still the same app,” the developer explains. “You already know how to use it. It has just been modified in a few places to better fit the form factor and platform paradigms.”

Arment also notes the challenges faced in preparing Instapaper for the iPad. The developer actually considered “a bunch of radical interface departures” but dismissed the idea early on. “I didn’t want to commit to any huge risks because I don’t have an iPad to test them on,” he concludes. He also wasn’t a fan of the way the current app looked when pixel-doubled in the SDK simulator, which is why he has worked so hard to deliver a native app as close as possible to when the iPad will be available.

Stay tuned for news on when the iPad version of Instapaper Pro will go live. We’ll be waiting!