Do it!!
I'm now up to my second iBook and second iMac (not to mention Airport Express and two airport cards...oh, and an iPod Mini) via the refurb store.
Don't let the quantity alarm you. None of these items crapped out. I'm a frequent upgrader and buy for my wife and myself.
Back to the products, they are first rate and brand-new in every conceivable way from the consumer stand-point. Plus, full up warranty. The ONLY difference you will notice is generic packaging versus Apple's usual hyper-spiffy stuff you get retail. For 20-35% off, I can deal with that.
I don't know why anyone shops elsewhere.