A different Joe Sheehan (who knew?) has a fantastic article up over at Baseball Analysts:
http://baseballanalysts.com/archives/2007/03/digging_through.php
Basically, ESPN is now tracking (and apparently making public) all sorts of new information, including data about pitch velocity, break, location and release point.

For the real diehards, there's a lot of new data mining possibilities. Hopefully they keep it up through the season, because it's the sort of thing that people much smarter than me can make into something really interesting.