Probably the tweak that I missed the most when I transistioned my iPad 2 from an iOS 4.3.3 jailbreak to iOS 5 was the lost functionality of Graviboard. I purchased this tweak from dev Conrad Kramer probably over a year ago for $2.99, and just applied a free update today. Overall, Graviboard works just as good as it did on iOS 4.
I have found that with paging enabled (grays out enabling the dock), I will sometimes get a crash to safe mode when changing pages. Otherwise, Graviboard has some nice customizations and is functions perfectly with paging disabled. I think my kids missed this activator function more than any other tweak I've had installed. One of the best reasons to jailbreak your iPad!