All the time I hear, "We're waiting to sell the house in the Spring market". Typically people percieve the Spring market to be in April or May. In my experience though, if you wait until then, you've missed the market!
I find that by mid February the market is already in full swing. The inventory levels are usually lower, which means buyers have less to choose from, alot of time creating multiple offer scenarios. By the time April or May comes, and inventory levels are higher, the prices tend to even out slightly and the buyers can take their time in looking for their new home.
Bottom line is - the best time for Sellers to hit the market is right now! Waiting a few more months will definately cost you.