[Update] This issue appears to have been resolved, and even without having to restore in iTunes.
Well this comes as a bit of a shock. It would appear that many users who are still on iOS 3.1.3 aren’t able to access the AppStore from their devices. A Discussion thread has been growing steadily over on Apple’s Discussion Forums on the matter so we’ll keep you up to date on if this gets resolved. For right now if you are on 3.x your only real way to manage apps is straight from iTunes I fear.
Problems faced by users at this time:
1) The price button no longer works
2) Ratings button no longer works
3) “Tell a Friend” and “Gift App” just jump to the top of the window
4) Images don’t load at all
5) Top In-App Purchases is just text now