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card tricks aren't math so much as sleight of hand and a few with counting.

David Blaine's watch trick (which I saw on TV a while ago with much better quality. good trick, too) is fairly simple, minus the window part. I couldn't explain the illusion there, but if you watch his hands rather than his face and where he directs attention, it becomes obvious how the watch 'vanishes' and then 'appears' again.

however, I'm not going to redirect this topic to explaining magic tricks. Magic, the so-called ability to abnormally affect the world around you, is uncanny in its ability to produce awe, however the only 'magic' that this one believes in is science (ironic, I know, since magic conflicts with the logic of science). Then again, logic is only what we make it to be, and is shattered by something that unequivocally refutes it.
Thus, I have no answer as to whether I believe in magic, but as for its existence, I would have to say only as what defies logic without fault.

This coming from someone who's brain can't wrap around the fact that something placed at the bottom of a mirrored bowl creates a 'hologram'-looking image. damn optical illusions...

It depends on one's definition of 'magic.' My teacher often said, "Magic is only science that we don't understand," and I have to agree if "magic" is defined as the one we see in Harry Potter or something like that. But if you describe 'magic' as the ability of such inspirational things as music or stories or whatever to bring happiness or understanding to people, then okay, I'd accept that as 'magic.'