I can pretty much guarantee you all that if Apple changes the resolution of the iPad it will be, like the iPhone 4, exactly double its current resolution.
1) If they maintain the aspect ratio and increase the resolution up to anything less than double, they can't scale it like the iPhone 4 otherwise you'll end up with graphic issues -- say they decide to go to 1536x1152 on the iPad, if you have an iPad app with a button on it with uneven dimensions, say 101x101, to upscale it to fit the new resolution it would produce 151.5x151.5, which just can't happen.
2) If they just make a new, higher resolution iPad which isn't necessarily in the same aspect ratio (but could be) iPad developers would have to support the old iPad resolution as well as the new, which is more hassle.
Instead of like on the iPhone where you make an app and just supply high res images and it's automatically scaled up for you on iPhone 4, you'd have to make two nibs, or maybe even two apps for the two different versions of the iPad.
The perfect and only possible resolution increase for the iPad is to 2048x1536 (264 PPI), no more, no less. I hope they can do it, because that'll be magical!
After reading this I now believe there will be no resoution changes in the current iPad. I was hoping for 1280x960, but now I see how that would make problems, and 2048x1536 would be too expensive and would put the MacBooks to shame. So no I think there will be no changes to resolution until Q1 2013.
Edit: on second thought... I was thinking old iPad apps could be ran in a window kind of with black bars all around the top bottom left right, like when running an iPhone app on an iPad, but then.... Like Steve jobs said the tablet would also need to come with sand paper...
My perfect world....
Q1 2011: apple updates the iPad with the expected changes...
Q1-Q2 2011: apple updates MacBook pros with ultra high resolution displays, with high performance gaming level gpus to drove them. Maybe they will even call it a retina display.....
And apple drops the price of the MacBook to 800. Then Discontinues it.
June 2011: iPhone gets even more thinner and lighter, minor CPU bump. Some other stuff
Fall 2011: iPod touch follows iPhone in it's footsteps, apple launches itunes cloud and wireless syncing, launches apps for apple tv, along with a Bluetooth controller for games.
Q1 2012: iPad gets a dual core, 1gb ram, and some crazy new feature that makes it more like it's running a desktop OS.
June 2012: iPhone finally makes the jump to 4g, retains the 2011 CPU, and some new feature.
Fall 2012: iPod touch follows the iPhone, iPod shuffle, and iPod nano, get built in wifi, for streaming and syncing. iPod shuffle simply straps onto your ear..... Apple tv is exploding as a family/casual game console, apple adds new features to add to that.
October/November 2012: MacBook air gets an even higher resolution displays to match the MacBook pro family, but a higher density on the 11inch. And speedy graphics to power the displays as Mac OS gets more and more games.
Finally Q1 2013: apple makes the jump to 2048x1536 on the iPad. And they will call it the retina display, and everyone will fight over the name retina display again.
Oh and I forgot lion coming summer 2011. And iPad and iPhone will get to verizon somewhere in there, but not exactly sure when or how.
......yea.... I got totally carried away... My bad.