I was thinking about this last night before posting today, and Greg has just mentioned a bit about what I was going to say in his last post. I'm going to attempt to comment on a few of the posts in one hit.
Brad, in answer to your first question. I think it is possible to "flip" uke with kotegaeshi in the street. I'll come on to how in a bit.
Nathan & Nick, that's true, but only if your focus is on twisting the wrist.
Greg, in answer to your first question, "why would allow them to escape like that?". Because I am practicing Aikido. There may be mitigating circumstances to not allow it (he's got mates, etc.), but generally, I would hope to allow it, and as you wrote yourself later, even allowing for the escape, you can still be winded and out of action for long enough.
Chris Gee, that's true, but Aikido movement is about you and what you do, not what uke does.
Chad, You can.
Kotegaeshi - I believe literally translated means to return the wrist. A lot of people get caught up in believing it means twist the wrist and rip it off the arm. Their whole focus in doing to the technique is trying to get uke to move by just twisting the wrist until it hurts. Which, as mentioned above, if done at speed could/ would induce a break, uke might fall backwards etc. When you apply it this way, people have often forgotten about their own movement, have rooted themselves whilst focusing on the wrist, and put themselves in conflict with uke.
Your movement is very important in Aikido, you need to keep it going through the technique until you have taken uke's balance, and through the combination of your movement and uke's momentum, put uke into the place that you want him to go. this can be a backward breakfall, straight down, or a "flip". You won't do this unless you move though.
In honest practice, uke wants you, he attacks you. You move and make hole, create a void and simultaneously manouver uke in to plug it. The difficulty is doing this without thinking about it, because the more you think, the harder you try, the quicker you stop moving, you become the conflict for uke's movement, we're back to focusing pain on the wrist to make it work.
I think that's enough waffling for now, it's Monday morning, I better get on and do some work.