Since it looks like a LOT of people seem to want/need JComments to work with Jomsocial, I decided to take a look at it out of curiosity (and a break from a very large component project that heavily uses JComments).
Maybe it would help if everyone gathered in one thread and worked together to get'er done.
I'll start by offering my own home-cooked Jomsocial Profile plugin for JComments
(please see attached ZIP file) Read the instructions. You will have to edit your Jomsocial template's profile.index.php file (and I suggest you make backups before doing so, just in case).
Please note that this plugin uses Joomla's native com_users table to actually do the integration (I'll explain if you're curious). If you take a peek into your JComments RSS file, you should see the correctly formed URL for Jomsocial profiles. Also, check your comments in the backend, and you should see that the item ID is the user id and the title is the username for that profile.
NOTE: The plugin only works on the Profile section of Jomsocial. To to a more comprehensive Jomsocial solution is not trivial and would require some time to develop.
Test before using this on your live server. I just put this together in a little bit of time and only did the most basic of tests. If there are any problems/issues/additional features, just post them here so everybody can have a shot at working it out.
Perhaps if we all put our heads together, we can get this thing solved community-style. Long live open source!