Regarding Mitt's tax return: While I'm not gaga over Romney as the likely Republican nominee - I prefer rough & gruff Newt - I think it is unwise for Mitt to reveal his tax return at this time.
Traditionally, candidates don't make their tax records known until sometime after the April 15th tax deadline of the voting year, and for my guy Newt and others to try and pressure him to do so is pure dirty politics and gist for the media hotplate. I also think it is totally foolish and unnecessary to reveal such information to the general public before there is more assurance of your party's nomination.
The former Governor is under no obligation to reveal his tax information at this time and he shouldn't bow to the political or media pressure to do so. If he is wanting to show he can be tough on principal this is a pretty safe and legal issue to do it on...show he has the cajones to stand up against his political foes and those forth estate rivals.