One issue I've seen since 4.0 on two different iphones (3GS and 4)...if you're deleting a few pictures, sometimes the bottom bar is not coming back up after you delete one or two. Just the top. This happens when I delete one, and then touch the photo to make the bars disappear to see the entire picture, and then touch it again to bring them up to delete it. All I have to do to fix it is hit the back button to go to the full album (camera roll) and then go back into the picture and the bar will show up.
Not a major bug, but an annoying one. Doesn't happen all the time so I can't reproduce it with any consistency.