It's hard to say. I've bought several refurbs from ecost, and for the most part they were fine. But some had some "quirks." For instance, one CD player I bought plays perfectly, but the display is bright enough to light the whole room! It's almost like there's no resistor/dimmer ahead of the LEDs. My other player (same model #) is maybe 1/3 as bright. Another CD player I bought there looked perfect and worked just fine- for about 8 months. Then it crapped out. Would a new one have? Maybe, but then I'd have had a warranty. On the other hand, I paid less than 1/3 of new price, so ultimately I think it was worth it.
My view is this- buy a refurb only if it's a cheaper component. Anything that would cost me less than $400-500 to replace, I'd take the chance. But I personally wouldn't risk buying a more expensive peice without a warrenty, especially a Denon. It's not that Denon are less reliable; but Denon will not honor the warranty unless you purchased from an authorized dealer.
Bottom line: buy from a local dealer. They'll often cut you a decent deal, too. I bought my 3802 locally, and I did need to have it serviced. I was profoundly glad I'd bought it at my local Ultimate Electronics. At least in my city, Ultimate bends over backwards to make sure you get the service you need. They're great guys. Not as cheap as an etailer, but they're there for you after the sale. I bought my DVD-2200 there, too. When I buy my next one, they'll be the ones to sell it to me.