1. It's the war, stupid. One of the few issues that McCain is actually 100% right on is the War -- the war in Iraq, especially, but the GWOT generally. For that matter, McCain is about as clear-eyed about friends and foes in a dangerous world as one can be. Obama is an utter fool in this regard. Even if he doesn't make us actually lose the war we're on the verge of winning, he will do us incalculable harm in foreign policy.
2. The Lefty-loonies are panting at the chance to remake America. Government-run health care, taxes all over the place (c'mon, aren't you "patriotic?"), loss of individual initiative in every area of life, a Supreme Court who makes it up as they go along, an "energy policy" that produces no energy but increases the price thereof -- that's what Obama stands for. The whole crowd standing behind him has spent eight years bitching and conniving and planning for the day when they take over. You really don't want that, do you?
3. The Democrats are utterly corrupt. The Dems gave us the housing finance bubble they now seek to fix. Pelosi has broken every promise she made in taking over the House. Reid is a disgrace. Earmarks abound.
Does this mean that John McCain has a better plan for America? Not particularly. McCain as President would muddle through, barely. He has several very honorable fixations which would serve us well, but he's never been a Big Picture guy. But winning in Iraq, vetoing the craziness coming out of Capitol Hill, and keeping Obama and the Democrats out of office seems sufficient for me to jump on the McCain bandwagon.