NEW YORK (CNN/Money) - With mortgage rates on the rise, it looks like homeowners are in a rush to take advantage of the good times while they can.

The back up in interest rates over the past half month has been furious. Where the 10-year Treasury yielded just 3.11 percent on June 13, now it is yielding 3.55 percent. According to Freddie Mac's daily data on where mortgage debt is trading (which is different, alas, from the rates you get), the rate on a 30-year mortgage has jumped from 4.5 percent to 4.99 percent. According to the Mortgage Bankers Association, the average rate on a 30-year mortgage rose to 5.23 percent last week from 4.99 percent just two weeks earlier.

And the response to this rise in interest rates? A rise in mortgage activity. The Mortgage Bankers Association reports that last week its Refinance Index bounced back after falling the previous week.

It's not hard to guess what's happening. When rates first began to climb, many homeowners reckoned that it was just a temporary move. They would hang back and wait for rates to settle back down again before they refinanced. But as rates kept on climbing, and as homeowners, perhaps, heard various talking-head Wall Street types opining that the bond bull market was done, they made the call to the mortgage broker.

If rates keep on moving higher we'll likely see more homeowners who have procrastinated on refinancing finally spur themselves to action -- a good thing, because the cash generated by refinancing activity has been one of the major fuel sources for the economy. But the last huzzah for mortgages won't last forever, and if rates rise quickly, it won't last very long at all.

Something will have to take up the slack. At least temporarily, the tax cut should do the trick -- in less than a month the Treasury is going to be sending out rebate checks to 25 million households.

But once that cash has coursed through the system, the rubber is really going to have to hit the road. If businesses haven't shifted out of their cautious stances, if the employment picture hasn't improved, the economy will be right back where it was in the fall.