They are reefsafe, but how much you see of it will depend on its roommates and where it chooses to make it's burrow. And be aware that they are the very definition of a jumper! Be SURE your tank is sealed off.
Good advice. I also know many people (myself included) who have lost one of these great fish due to a mysterious white fungus. If you're planning to get one at the LFS, I would recommend asking them to hold it for a few weeks...and inspect it carefully (if possible, that is) before bringing it home. Technoshaman is the only person I've heard of that has had a BSJ recover from this ailment...I'm hopeful he'll chime in here.
Good luck...they are truly fantastic fish. They are also reef safe, btw.