You even could push it to the new law's actual date. "If you can move into the vacation home on Jan 1, 2009," says Olivieri, "you can sell the house and claim the full gain exclusion as long as you meet the requirement that you live in the home for two out of the last five years before the sale."

Be careful, however, if your second property was rental real estate. You will still be required to recapture depreciation you claimed on the property, says Scharin.

On the plus side, though, the new law grants an exception for "nonqualified use," or any time when the home wasn't your principal residence, if the house's original use was as your main home. A period of absence generally counts as qualifying use if it occurs after the home was used as the principal residence.

This exception could come in handy, for example, if you moved but were unable to sell your home because of a slow real estate market. Although technically the property is no longer your main home, since it started out that way, you don't have to factor out that non-residential time, or nonqualifying period in tax-speak, when you do eventually sell and realize a gain, says Scharin. Of course, you do have to meet the other home sale exclusion rules, such living in the home as your main residence for two of the five years before the sale.

A new loophole

There's a way, says Olivieri, that current owners of both a primary residence and a vacation home can sell the properties and claim the full tax exclusion amount for both. He offers this example:

You have two homes, one clearly a primary residence and the other clearly a vacation home. On Jan 1, 2009, you move out of your principal residence and into your vacation home. You don't have to sell your original principal residence yet, just move out of it.

Live in what once was your vacation house, but now your main home, from Jan. 1, 2009, until Jan. 2, 1011, to meet the two-year residency rule, then sell it and claim the full gain exclusion. Remember, if you have a gain in excess of the $250,000 or $500,000 exclusion amount, you still owe tax. But there's nothing to prorate because you converted it on the new law's effective date.

When you move back to the original primary residence, you can sell it and claim the full exclusion as long as you meet the tax rule that didn't change: You live in it as your main home for two of the past five years before the sale. You can't move in after 20 years, sell the next day, and get the full exclusion.

"You don't have to prorate the exclusion to any period that it was not your primary residence if that period occurred after a period when it was your residence," says Olivieri. "It is a new loophole, but one that was intentionally done."