Seemingly everybody else has written nice, in-depth previews, so rather than writing my own, I'll just leech off of their hard work.
INCH previews the East, West, Midwest, and Northeast Regionals.
Hoover Street Rag has a very thorough breakdown of every team in the tournament.
MGoBlog looks at The East Regional.
Bruce Ciskie is writing previews over at Fanhouse. The first up in on the East regional. Here's the West Regional, Northeast Regional, and Midwest Regional.