I did the numbers on the McCain health care proposal for the folks at my company, based off the new health insurance plan they're rolling out next month. Looks like it's a slam-dunk for me, personally - my total-cost-to-company is less than the $5000 credit, let alone the after-tax cost which would be incurred under the McCain plan. The full-coverage all-family plan is about three times more expensive, but it's still far and away neutral & the marginal tax increase caused by making the plan & employee contributions after-tax would be more than covered by the $5000 credit. In fact, the plan cost would have to be increased radically to incur an actual net tax increase.
Mind you, my company plan isn't particularly stingy. It's a good plan, from what the folks with families and kids say. Personally, I barely consume health care myself, and what I do is minor stuff out of pocket.