1. Rafael Soriano's strengths/weaknesses?
Soriano's strengths are pretty typical for a dominant reliever: he strikes out a ton of batters (8 K/9 last year, 12 K/9 in 2009) while limiting walks and hits, and he keeps the ball in the park. He has three main pitches: a 93 MPH four-seam fastball, a 91 MPH cutter, and a 83 MPH slider. His fastball is his main weapon (especially against lefties), and he frequently uses his slider as his out-pitch.
As for weaknesses, Soriano is a flyball pitcher, but his HR/FB rate is normally below league-average so it's never been that big a deal. I'm not sure how being a flyball pitcher will play in Yankee Stadium, but I wouldn't be worried about it; Soriano is still a beast. His biggest issue has always been his health: he's had a load of arm injuries over his career, and he's never gone three years in his career without suffering some sort of injury. We got lucky with him last season, but it's really tough to tell how his health will be going forward.
2. How do you think Soriano will play for the Yankees?
I think he'll be awesome for you guys. MFIKY became a favorite among the Rays' fanbase last season (cue "I didn't know they had any fans" jokes), and you could tell that despite his outwardly calm demeanor, he was a raging cyclone inside. He gives pretty hilarious post-game interviews, and his shirt untucking became a team-wide phenomenon. I don't know if the Yankees let their players untuck their shirts on the field after a game, though, so I suppose that could dramatically affect his play (/sarcasm alert).
Enjoy Sori - he's a heck of a player. As long as he's healthy, he'll be the best 8th inning guy in baseball.
Thanks to Steve for the answer! The last sentence is exactly what I wanted to hear.