I would make sure before I placed the order that somewhere in the order or on the receipt it states that it is an out of the box purchase and whether or not it is under warranty and returnable the same as a unit in the box. I've dealt with Newegg before and they are a reputable company. I have not, though, ever gotten any type of out of box deal. Just make sure it's all documented and you should be fine.
Speaking for experience. HELL NO. Just think you put it all together and something is wrong. Something? Well if it's the motherboard you can pay to send it to to ASUS for RMA. You won't get a new one back. You can return to newegg.
I, for one, would never order "opened box" merchandise unless I could inspect it before purchasing to be sure it was in working order.
I am however curious as to what NewEgg's opened box process entails. Do they test the returned product before reselling. If so, how extensive is this testing? Does the opened box product come with a different warrenty than new?
In the past, I have suspected that even some of my "new" goods ordered from Newegg were returns. No solid evidence, but I have noticed some wear and stickers missing/poorly attached on some "new" stuff I've gotten. I know this is illegal, and Newegg must disclaim returned merchandise before reselling, but I wouldn't put it past them (even though they seem to be an honest company).