Feargus Urquhart (spelling?), Scott Warner, Jason Manley, the list goes on...
Alot of exceptionally tallented people have left Black Isle Studios in the last few years, the three above are some of the more notable ones I can think of off the top of my head. I'm missing some other big names no doubt, and alot of names you don't hear about so much either. Now Josh is gone too...
I think the fans though are reading too deep into this. Changing jobs after a few years isn't an oddity in today's economy-- a five year stint at the same company is quite a long tenure nowadays. It just seems that BIS can't keep a hold of any of their top talent, thus feulling the rumor mill. They were a great company, having produced three of the greatest and non-traditional role-playing games I've ever played: Fallout, Fallout 2, and Planescape: Torment. But in all honestey, they haven't developped a game I've been impressed with in over five years now, and none of the recent games have been innovative.
Many of the people who have left cited or hinted at problems with Interplay (Black Isle Studios is the role-playing game division of Interplay). Plus Interplay stock has crashed, they were even delisted from whatever market they were in. The company has been sold off, the 'new' parent company (was Titus, not sure if it still is) wasn't too happy for a while...blah blah blah. The rumor mill goes on, but I didn't pay any attention to that, I haven't frequented the official BIS forums since the Torment days.
Either way, many will say it doesn't bode well if you're hoping for an innovative or original game from BIS. Then again, back when Fallout was released, Cain, Taylor, et. al. weren't exactly huge names in games, and the title sorta came out of nowhere. There's nothing to say that another quality game can't come out of the studio, despite all their current big names leaving for greener pastures. I'm sure there's still alot of talent left in that division...we'll see.