Right now hes behind Durham at 2nd. He doesn't really have a position defensively. He's kindof a butcher in the field, often booting the routine play. At one spring game I was at, they even had him taking fly balls in the outfield.
He'll see some time especially with the off days Durham needs and his propensity for getting hurt. Speedwise, there are few in the game that can run like this guy. Physically he's all skin and bone. If he could hit a little and play average defense, he could steal 60 bags in his sleep.
When he plays, he will get plenty of steals, but thats still an "IF". The giants, atleast to start the season, are going with the old guys they gave too much money. That means Dave Roberts, Randy Winn, Ray Durham, and Rich Aurillia will all see plenty of time. As the season goes on, he will get more time, as will Freddy Lewis and Raja Davis.
But as others said, he is only steals, thats it. And this he will get very inconsistent time in field(atleast until Durham hits the DL), I don't know if I'd pick him up yet, but if you're really desperate for SBs, I'd definitely keep an eye on him, and as the aging giants proceed through the year, he will get more time.