Is a 2007 or 2008 too old for a used car?

I'm looking to buy a Toyota Camry XLE or Honda Accord EX-L and I really don't want to pay over $20,000 for one, so I'm thinking about buying used. I won't be buying until later on this year or early 2011 so the 2008 models might have gone down by then, but right now a 2007 is in my budget. Is 3 years old too old for a used car? I'm planning on buying from Carmax and getting a Carfax report. Please don't tell me not to buy a Toyota. Just answer my question and provide some input on buying used versus new. I'd love to hear from people who brought a used car and felt that they made a good decision.