If you've been thinking that you wanted to take advantage of the first-time homebuyer tax credit, note that -- as of this writing -- it runs out this year. And note that "this year" means "November." That's right, to be eligible for the credit you have to close, not by December 31, but by November 30. Add in the time it takes to get a mortgage, and this is really your last month to shop.
Now, we have a maxim in the real estate industry that property is one of the few things that people don't like to buy when it's on sale. I think some buyers feel the same way about a sense of urgency. The same people who would drive to the grocery store to get a Sunday special on a ham don't want to hear that they really ought to be buying a house in November. However, if you can snag the $8,000 tax credit (it phases out as income rises, so singles who make more than $75,000 and couples who make more than $150,000 in adjusted gross income aren't eligible), you should.
If, on the other hand, you're in the starter home niche but you're not a first-time buyer, it might make sense to wait until November to make offers, because you'll be facing less competition that way.