yaix2 - 2:54 am on Jan 10, 2011 (gmt 0)

If you add all favorites as a comma separated list into a user's table row, then it is not possible to search, on who's favorite list a particular user appears. You may want to tell a user "you are on these people's favorite list" so they can add them as well.

So its definitely better to put it into a separate table. The favorites table would be very small anyway, two INT columns probably, with the two user's ID numbers, and both should be indexed.