That's a really good question, Jim. The tax credit is, to me, a short-sighted reason to buy. The important stimulus package ends on March 31.
The Federal Reserve has been THE buyer of mortgage bonds for over a year. They've spent (most of) $1.25T, they're done in March and all reports that cite Fed governors say they're thinking a +/- 1% mortgage rate increase is coming. That would then apply to all buyers in the April 1 - June 30 period.
I don't see how you "win" by writing a contract on April 30th for a June 30th close. Let's ignore any possible increases to home prices from now until June and compare today's rate versus June 30th's. Interest expense on a $300k loan over 5 years:
--Rates up 0.5%: Cumulative interest is ~$7,200 higher.
--Rates up 1.0%: Cumulative interest is ~$14,500 higher
--Rates up 1.5%: Cumulative interest is ~$22,000 higher
Over 10 years the numbers are staggering. Moral of the story: I think the people that closed this month or last are the big winners on the tax credit--both the $8,000 and the ~5% mortgage rates.
Just my $.02,