I think if I had it to do over again I wouldn't have upgraded. I was hoping that the atrocious iTunes would be significantly improved in conjunction with iOS 5. No such luck. The other "improvements" are more than balanced by the imposition of Apple's god awful version of Publisher's Clearing House (without sweepstakes) otherwise known as Newsstand that clutters my screen like the PCH crap clutters my snailmailbox.
The split keyboard is, I suppose, a bit of an improvement over the virtual keyboard but since I rarely use the on-screen keyboard at all, it's not worth it to me.
Otherwise, no significant improvements over 4.3.5 that I was running prior to the upgrade.