My iPad 1 has the same issue, started recently. For example, I'll click on an app and it appears to be opening, but then it reverts to the app list page. After 1 or 2 tries, generally the app will open, but not always.
Have had this happen on Angry Birds, Slate, Huff Post, NYTimes, the Weather Channel app and others. I have the 16 G iPad w 3G, updated/synced regularly, and note that I'm down to 2.5G of available space.
Any ideas?