Yes! I thought it was only me...
Since I upgraded to iOS 6 the autocorrect has gone way downhill on my iPhone 4S. It used to correct a solo i to uppercase I but it doesn't now. It used to have trick like correcting "welll" (with triple l) to "we'll" but leaving "well" alone. Now it will only correct to "well". It used to do the same for "he'll" and "he'll" but now it corrects both of them to "he'll" - the opposite behaviour.
I know it learns as you type, but this is new behavior that only started with iOS 6. I've been using an iPhone since day 1 in 2007, so I don't know if it only brought over part of the learned autocorrect behaviour at the last update or something, but it's so annoying. Things that I'd got used to not having to correct now come out wrong and some things get "corrected" from what I intended to something wrong.
I think I'll try turning off any shortcuts I taught it, and probably wiping and resetting the phone, but if it is a bad transfer, I've probably already over written any backups with this new behaviour...