As far as I know, Apple gives the entire system a thorough check and replace any components that are problematic. Couple that with the same 1-year warranty as a new unit, and I find its a great deal. I saw this same exact configured system on Amazon for $600 more (Apple says its $400 off the original price). Mine came looking brand new. They do ship them in different boxes than the new systems (I suspect so people cannot pass them off as new).
One thing to be aware of is that some resellers do their own "refubing" - I cannot speak to the quality of those units. I've only purchased refurbs directly from Apple.
I'm using it right now, but only to do some additional research (my old system is unhooked @ the moment). I just installed an extra 8GB of RAM and am looking at different hard drive configs to figure out what will work for my needs. I want to get all of the upgrades in place and reload the system before I start transferring everything over from my old system. This will include swapping out the factory HDD for a new one. I'll probably use this one for backup purposes and add another 1 or 2 internally.
I'm itching to completely phase out my old system, but I suspect its going to take me a good week to get there. But at least its FUN to do that ;-).
