MLB.tv isn't terrible. Their interface is actually quite nice, except that it only works properly in Firefox. The blackout restrictions are so-so, all local market games are blocked, as well as Saturday afternoon (FOX) games and Sunday Night Baseball (ESPN). Basically its not a bad deal if you don't live in your team's local market, especially if you are like me and can easily spend an afternoon watching every NL game.
From what I understand, MLB is better, but I can't speak from experience... curious if anyone has any comments...