Today, a Serbu page says the weapon will hopefully be selling by the end of 2006. (Guess the page needs to be updated.)
Jeff @ Alphecca test fired the bolt-action BFG-50 in SEP '05, and enjoyed it.
Incidentally: Images of a bolt-action Serbu being built, posted by Mark Serbu.
For those of us not in combat situations, and only desiring to bust up inanimate junk, the extra cost of a semi-auto .50 is not justified, and the motion of heavy metal near one's head can be done without.
Any .50 you'll want to fire more than once is going to look and feel like a big pipe.