This article is from the R.E.M. FAQ, by Ron Henry (email@example.com) with numerous contributions by others.
Peter Buck said this as an off-the-cuff joke during an interview (mainly in
connection with it being a great excuse for a huge party), but they have
all repeatedly said since then that as long as they feel R.E.M. is making
good music, they will continue to work together -- whether that doesn't
last until 1999, or goes beyond. Note that magazine writers who can't think
of anything else to say about the band will often trot this factoid out and
compel the band to comment on it.