I've discussed & recommended RetinaPad in several of my articles, which makes it possible to run most native iPhone apps in high-resolution mode on all iPad models under all iOS versions - something that Apple should have done in the first place.
The new, currently-released, 1.3 version is buggy. It has completely messed up my iPad2 running 5.0.1 making it almost useless (the interface is like a big iPod touch now; stock apps don't work, many buttons / UI controls in third party apps don't work either etc. and RetinaPad can't be uninstalled via Cydia either as the "Remove" button doesn't work either) and, according to the dev's Twitter feed, at least two other devices. Currently, there's no known way of fixing the problem and it's not known whether it is at all fixable without completely wiping out and reinstalling the device. Which isn't very good news for anyone, as the new, 5.1 version of iOS, currently, can't be jailbroken.
Again: In no way upgrade to 1.3!
UPDATE (10:32 EET, the same day): fortunately, the dev fixed the problem. Now, you can safely install the current, 1.3.2 version from Cydia.
If you've installed 1.3 and suffer from the same "big iPod touch screen" problem, do the following: do NOT try upgrading from inside the app description screen as the "Modify" button won't work there. Just let Cydia find the upgrades under the "Changes" tab and upgrade all. There, the button will work - unlike with the app screen.