I and a guy at work, bought an iMac G5 Refrub from the Apple store. Mine came and all has been fine, just like a new system. The guy I work with, he bought a refurb extreme card in addition to a refurb iMac G5. When he got both of them in, he noticed the extreme card had a weird dent in it. Thinking it was just refurbed and not a big deal, he installed it. When he installed it, he noticed the power supply wasn't secure in all the way. So, he put it all back together and had issues with his wireless networking. Then, his computer started randomly shutting down and pretty soon it wouldn't stay on for more than 10 minutes.
Apple gladly replaced the card and the power supply and all is good now. But, this guy was a switcher, so it wasn't the best experience for him, but he is happy with the results.
I can't afford to always buy something NEW so getting a refurb is the best I can get and still save some $$$.