I have a post up over at Greg's place suggesting that the president use his budget speech on Wednesday to hit Paul Ryan and the Republicans over the phony numbers in their "budget." For the full argument, head over there.
But for the point that real numbers right now help the Democrats, see Nick Beaudrot. As he points out, the goal that Republicans have set for themselves (mainly balancing the budget while cutting taxes) is basically impossible to do without seriously putting themselves at serious risk by endorsing spending cuts that people really care about. Unless, of course, they cook the books. Rather than getting into a bidding war with Ryan at this point, Obama's best play is to try to win budget idealists over to his side by emphasizing that Ryan hasn't done what they're giving him credit for. If he tries to compete on deficit reduction while using honest numbers while the GOP uses Stockman/Daniels projections, he's apt to lose both the substance and the spin war.