Here's what I think.
First:
Mitt has refused to show his taxes because he knows that he's one of the 47% that doesn't always pay tax. All we know is that he paid taxes for one or two years: years that he was campaigning.
Mitt's wealth allows him the shrewdest and least ethical accountants that money can buy.
Second:
I want a president who isn't afraid to tackle the hard questions even when it requires getting dirty and taking a lot of abuse.
Mitt's excuse for not showing his taxes is, in part, he doesn't want to provide his opponents with ammunition. In my mind that tells me two things. One that there IS something unseemly in his taxes (like there are years when he didn't pay any) and two, he's spineless and doesn't have the personal strength to deal with abuse, like the kind he and his party heap on Obama every day.
There is no way in hell that I'm going to vote for a cowardly candidate that refuses to share his taxes with the electorate.