Well, it isn't, obviously, but it certainly is an issue that is important.
Obama has been criticized as planning to raise your taxes while McCain will cut them... the LA Times the other day published this chart, showing how your taxes would be affected if either candidate's tax policies were completely adopted.
Unless you're in the top 20% of incomes, you get a larger break with Obama. Now, if you're in the top 1%, then McCain is definitely the man fr your pocketbook.
And speaking of the top 1%... you've no doubt heard McCain's comment that he didn't know how many houses he owns. Here's a video to help him out...