After upgrading to 2.8, comment editing does not work.
To reproduce it, change an already approved comment and save your changes. You've got this error message:
Warning: array_merge() [function.array-merge]: Argument #1 is not an array in [path]web/wp/wp-includes/comment.php on line 1097
Warning: Cannot modify header information - headers already sent by (output started at [path]web/wp/wp-includes/comment.php:1097) in [path]web/wp/wp-includes/pluggable.php on line 865