The nonpartisan FactCheck.org criticizes both Democrats and Republicans in their characterization of the tax components of the Democrats proposed 2008 budget in Counter-rotating Tax Spin:

Does the Democratic budget contain the "largest tax increase in American history" or "not one penny" of increase? Answer: neither.

Summary: The Democrats’ proposed 2008 budget is being spun by both sides. Democrats claim it will not raise taxes by even a penny, while Republicans say it will impose the largest or second-largest tax increase in history. Obviously, the budget can’t be the largest tax increase in history and zero tax increase simultaneously. So which is it? The answer depends on a couple of questions: What constitutes an increase? And an increase compared with what?

The budget does not propose a new tax hike, compared with current law. It would, however, allow many of President Bush’s tax cuts to expire, meaning some Americans will pay more compared with what they pay now. We suspect that those affected will see that as a tax increase, contrary to the Democratic spin. But the Republican claim that it would be “the largest in history” is off base, too. Measured by the yardstick most economists favor, it’s not even in the top 10.

For the detailed analysis, see here.