I've owned seven Macs - all but one (my current Macbook came from BestBuy) came from various eBay sellers. I, like Cassie, don't see the need to pay full price (for anything, acutally) when last year's model will suit me just fine. Hence, I usually buy on eBay - and save money. My Macbook, though, was a clearance model - so the same applies, even though it was "new." 😀
I only recently replaced my Mini with a white iMac because the Mini's graphics wouldn't cut it (I wanted to run AOE3 and get rid of my last PC). So I sold my Mini first for about $550 with monitor and all, then used that money to buy the iMac. I had planned on a refurb, but I couldn't justify the extra $350.