It also hasn't been litigated in the courts. The case isn't ripe until 2014, when the first tax bills come due. Until then, no court action can happen. Somebody has to pay before anybody has any standing. I wouldn't be surprised to see the whole law tossed out then because it's a poll tax.
Nope, the SCOTUS majority said that the mandate was not a tax for purposes of the Anti-Injunction Act, so that challenges to it were ripe now. It then went on to hold that it was a tax for purposes of the Constitution, and upheld it as not being a "direct tax."
The 24th Amendment doesn't come into play here, because not paying the penalty doesn't take away your right to vote.