With Edit Comments XT I've released a new plugin compatible with WordPress 2.1.x and 2.2.x.
Edit Comments XT is a simple WordPress plugin that allows commenters to edit their own comments. To edit a comment, a user must have the same IP address as the user that made the comment and they must also make the edit within a specific time frame. The default edit time window is 30 minutes, but it can be changed easily in the plugin’s option page.
Edit Comments XT is based on Andrew Sutherland’s great Edit Comments plugin and works with WordPress 2.1.x and 2.2.x. Also, the security issues of Andrew’s plugin have been addressed & resolved.
There is also the "Ajax Edit Comments" plugin out there, however some users I know did experience char set issues. Anyway I think the main problem of Ajax Edit Comments is that it does not work with every theme and that you can't place its edit section where you want.