What's the difference between a private jet and a fancy vacation home?

Under the new budget agreement, one is subject to a new luxury tax and the other is not. The proposal would impose, for the first time since 1965, special taxes on the prices of some goods simply because they cost a lot of money.

It calls for a 10 percent tax on the amount by which the purchase price of certain items exceeds a particular threshold. Those items and thresholds are: jewelry, $5,000; autos, $30,000; yachts and boats, $100,000; private planes, $250,000. Planes used 80 percent for business would be exempt. The threshold for furs was still being debated.

The taxes would bring in between $2.1 billion and $2.8 billion in new revenue over five years, depending how congressional negotiators resolve the final details. Other playthings of the rich such as thoroughbred racehorses, designer clothing, second and third homes, original art, silver and crystal are not covered by the new taxes.

The Internal Revenue Service might find it difficult to enforce the luxury tax, some experts fear.

"There is clearly an incentive to break these articles into smaller pieces and sell them separately," said Randall D. Weiss of the accounting firm Deloitte & Touche. "The question is, is it worth a second trip? Will people come back later to buy the spare tire or the stereo to save 10 percent?"