I have not personally used the Touch (other than looking at it on display at Target), but I have the Keyboard version so I can tell you a bit about that.
Main things I use the keyboard for are typing in the password to unlock my Kindle (you don't have to use the lock feature, but I do), typing in a web address when using the browser, typing in a search term when shopping in the Kindle store.
I actually thought about getting a Touch too when they came out. I liked the idea of just tapping the screen to turn the page, vs hitting one of the side buttons.
The side buttons on my Keyboard are my least fav feature. I don't think they are in the right position to really benefit single hand use of the Kindle (I think they should be higher up the body of the Kindle). I also find that very occasionally, when trying to use the Kindle Keyboard with one hand, I accidentally slide the on/off. Of course these issues could just be my own poor coordination!

The above complaints are just minor things though, and I really do LOVE my Kindle!