As Marilyn Kennedy Melia points out in her article, "1. Change, 2. Choices," you can now find agents to help with short sales, foreclosures, buying or selling a "green" home, and more.
Meanwhile, other agents have (according to seemingly good authority within the article -- namely me!) packed up their offices and headed for careers with less uncertainty and competition.
Marilyn also quotes me as saying it's worth asking agents about their negotiating style before signing them up. Indeed, carefully observing an agent's personal style and trying to get a handle on how he or she will represent you in front of the other party is particularly important for both buyers and sellers, because negotiations can get contentious.
Buyers have leverage in today's market, and they know it. Many deal have fallen apart over amounts of money both large and small, for example because the buyer negotiated hard over repair costs after the home inspection. It's all too common for either the seller or the buyer -- or both -- to start to "take a stand" on mere principle, forgetting that the ultimate goal is to transfer the house.
WIthout a skilled agent to smooth relations with the other party, not to mention provide a voice of reason when you yourself most need it, a deal that looked rosy one day can simply wilt and die the next.
By the way, I've got a whole list of other questions you might want to ask agents before signing them up -- you'll find it in the article "Choosing Your Real Estate Agent."