The same interest rate today will probably cost you about .25 less than it did yesterday.  This is due to the market gearing up for what it hopes will be a bond-friendly announcement from the Fed (recall that mortgage bonds are directly responsible for interest rates.  The higher the price of bonds, the lower the interest rate.  So "bond-friendly" for traders is good for you).

Traders are hoping that Bernanke will give as firm a verbiage as possible indicating future rate cuts are unlikely.  This will ease the market's mind about inflation, which is an arch-enemy of bond pricing.  

Mortgage rates have pushed into such a nice territory this morning that it may be best to lock unless you firmly believe that Big Ben will in fact say 2 things:

A: No more rate cuts

B: Inflation will continue to moderate

If he does, floating your rate, although risky, may be worth it.  Still, if we go strictly by historical numbers, we're in the area now where we've encountered precipitous resistance in the past, making the safe bet to lock this afternoon.  Can rates improve the rest of this week?  Absolutely, but they can get worse even quicker if we don't get the data we want.  If you want to "let it ride," stay tuned to the professional blog throughout the day and make sure you are ready to lock your loan at a moment's notice.