If you take a look at Facebook’s Developer Roadmap at http://developers.facebook.com/roadmap/, you should mention that “Comments v1 migration” will be carried out at “April 29, 2011”.
However, it seems to be postponed.
For my FAQ site, I can still use that the v1 comments boxes are used. Sample pages include http://www.takwing.idv.hk/tech/fb_dev/faq/general/gen_11.html. If v2 is used, I would expect I can “reply” to comments written by other users.
I don’t mind if the migration date is postponed… but I would expect an announcement or update in the roadmap.