Also, most common rich text formats don't play well with the diff format, so it can be difficult to see changes in a meaningful way. I actually hope to work on a solution to this problem as a school project this fall, so if anyone has any suggestions, I'd love to hear them.
Other than that, most version control interfaces leave something to be desired. They are natural for us, but not for most other people. I realize that there are some good tools available, but I haven't seen enough of them to say whether or not average users could get used to them.