I like this move. Keppinger (31) is a solid, versatile player who makes a lot of contact and can hit for average. He can back up short and third and I would expect to see him get the lion's share of ABs at 2B from here on out (assuming Sanchez does not return). He can also play the OF and 1B in a pinch.
Henry Sosa (25) was once one of the top pitching prospects in the organization, with a plus fastball and a plus curve, but he has been plagued by injuries and inconsistancies. He was simply awful earlier this year at AAA-Fresno (10.41 ERA in 17 games) before being demoted to AA-Richmond where he bounced back a bit (2.68 ERA in 40.1 IP). This is the best possible move for Sosa, who was unlikely to crack the rotation in SF any time soon and was, at best, a bullpen arm for the club. He undoubtably will get a look-see this year in Houston in what could be viewed as a make-or-break season.
Stoffel (22) was seen as a future closer when he was drafted in the 4th round of the '09 draft and is the player in this deal who is most likely to come back to bite the Giants in the butt. He has racked up 38 saves this year and last (13 this year) but has had some control issues and has given up a lot of hits (9.1/9IP). Coupled with the emergence of Heath Hembree, Stoffel had become expendable.