Also, you unlock the Armory, Cantina and Research Lab after the first few mission, leaving you with tons of upgrades to your structures and units.
I won't start competing on Battle.net until I've completed the campaign and fully mastered the game (e.g. keyboard shorcuts). Why? I actually want to participate in the upper tiers of the game. I hope this will come with lots and lots of practice and battles against other players. However, this may never happen. Who knows?
Stay tuned.