Mark
CreativeMountainGames.com
In the past we've occasionally had people using XP comments to be jackasses, thinking for some reason that it was okay to be insulting if it was in a comment. These are now highly visible, making it much easier for the Moderators to address the problem*.
* with a short sharp kick in the NADs.
No doubt that neg rep will wind up being used in that manner. The bandwagoning effect of having rep comments visible in posts and the cliquishness it will likely engender are going to be problematic, too.