You can add comments on changesets/shelvesets in web access, with TFS 2013 preview. This again a very effective way to communicate more information on the changes made in the changeset in addition to the default comment.
It is very simple to add a comment and it is possible for you to modify/delete the comments added on changeset/shelveset. May be this can even be used to do code reviews on changesets.
Let see how to add comments
1. Go to web access Code--> Changesets and open a chageset. you can see comparison view of the code files modified. Highlight a portion of code and click on the small icon appear on left side of code.
2. Type in comments and hit Return key to save.
Any other team member can reply to these comments. Unlike the team room chat this is not recorded as history. If you delete comment it is completely deleted.
Only problem I see with this feature is that you cannot view this outside of Web Access. Simply you cannot see these comments in VS when you view the changeset.
Still it is a cool feature comes with TFS 2013... and await for more...