Are Realtors Worth Their Commission?

Lately there has been an assault on the Real Estate industry from all sides.  Online home evaluators like Zillow.com claim that most of the services Realtors used to charge for can now be found free of charge on the internet.  My question to all buyers and sellers out there is - what do you think?  What is your current opinion of the real estate professionals in the industry and what experiences, good or bad, would lead you to choose or not choose to use a real estate professional for your future transactions?