Sorry, did not read all the replies... but..
In my opinion if you want to boycott Activision, you should BUY Starcraft II.
Seems weird? Yes, but let me explain.
In the Activision-Blizzard merger what happened? Activision leader, Bobby Kotick got placed CEO of the whole company while Blizzard's CEO got to keep his job as leader of Blizzard. If you check the financial results of the last quarter you will notice that Blizzard revenue (yes, they still keep them separate) INCREASED while Activision's decreased sensibly.
The more of Activision's revenue is due to Blizzard, the more power Morhaime can gain out of the deal. Infact, if Blizzard products would remain competitive while the other Activision products would plummet, you can be sure Vivendi, that own them both, would kick out mr Kotick and place the whole thing in Morhaime more than capable hands.
Oh, btw. Sc II has an offline mode called "Play as a guest" that, if I remember correctly, does not even require you to sign in on Battle.net but of course does not give you any achievement but should permit you to play the whole single player campaign no problem. I do not know if you need to be online for it to work or not.