When is the best time to move? I get asked this every week, if not every day. My advice is simple. Move when the time is right for you. That may sound like I'm dodging the question, but the point is make sure you are moving because of reasons that are important to you.
With the Tax Credit expansion and time extension, right now *is* a great time to make a move. Make sure it's the best time for you. If you are already thinking about it, then yes --- it is probably a mistake to not start the process right now. Today. No sense in buying a home 10 or 60 days after the Tax Credit deadline.
Besides the Tax Credit scenario, I am often asked what time of year is best to buy or sell. Honestly, it's up to you. The home that is perfect for you (location, price, etc ...) could be available today. It might not go on the market until June.
Most people start things in the Spring. It's human nature. Spring is a great time to market a home. The trees are getting leaves, flowers are blooming. On the other hand, there will be more homes on the market --- in competition with your home.
From a Buyer perspective, same thing. You get to see a home's landscape in full bloom, water problems can be more evident, and it's generally more pleasant than traipsing around in the snow. However, there are more buyers. You will have more competition.
With few exceptions, time of year shouldn't be your deciding factor. Time of life should be.