As an Orioles fan, I saw Sosa play a lot the last season he was in the game, 2005, and his spot in the lineup was a huge weak point for the team. His skills just seemed to free fall all at once that season, and a year older and a year out of the game, there seems to be little reason to think he can regain much of his former glory. I think he's never been the same since he got hit in the head by Solomon Torres on a pitch that shattered his helmet. Now, he stands too far away from the plate and can't reach a lot of pitches.
Understandably, the prolonged slump he went through in 2005 crushed his confidence, so it'll be interesting to note his mental state when and if he comes back. If Sosa has anything working for him, it's the fact that this is a no-pressure situation for him, because not much is being expected. Just don't count on him being the kind of player he once was - he needs to find a niche on that team, like part-time DH, to be successful. But for a man with the healthy ego that he has had, that might be a tough pill to swallow.
But then again, so is the professional state he finds himself in now.