Sonia Sotomayor was officially announced by Pres. Obama as his first nominee to SCOTUS today (5/26/2009). Her professional credentials fairly mirror Justice Alito's, and from what I can tell, her rulings from the bench are fairly close to those of Justice Souter. My biggest problem with her is that she seems to believe that empathy and identity politics have some place in making judicial determinations and rulings of law.

Here's a roundup from SCOTUSblog of some of her rulings and the relevant dissenting opinions as well.
http://www.scotusblog.com/wp/?s=sotomayor

I also recommend keeping an eye on the Volokh Conspiracy for more legal analyses of Sotomayor.
http://volokh.com/archives/archive_2...tml#1243349566
http://volokh.com/archives/archive_2...tml#1243348317
http://volokh.com/archives/archive_2...tml#1243346531
and more.