I've probably purchased $10k+ of refurb stuff from Newegg through the years.
I've had stuff that was DOA and stuff that died too soon. I've also had stuff that still works to this day. Most items purchased were video cards and motherboards, followed by hard drives (BITD there were some great refurb deals on HDDs at Newegg). Also had gotten a couple of random CPUs, RAM, cases, SFF barebones, sound cards.
SFF barebones: Some missing accessories, one DOA, one died in few days, one bad AGP slot (but Shuttle fixed under warranty). Probably close to 10 units total, so around 20% failure.
Sound cards: I think I only got one ever, and it still works (Chaintech AV710).
Cases: Got an Antec 1080AMG that was fine, with a working TruePower PSU. Got an AOpen A600B case that was fine except missing 5 out of 6 of the front drive bay covers. Incidentally the AOpen case came with a previous-user installed ATX I/O shield that was a match for a refurb motherboard I purchased around the same time - coincidence?
RAM: Had a couple of good sticks and one DOA dual channel pair, so probably 25% DOA.
CPU: Had one unstable chip. Don't remember how many I've ordered but it wasn't that much, so probably had to return about 25%.
HDD: I've purchased probably 12-15 HDDs as refurbed from Newegg and to my knowledge every single one of them is still in operation to this day. Some of the WD drives had the word REFURBISHED printed as a watermark diagonally across the label in light blue, but otherwise the drives have all been fine. Have gotten WD, Maxtor and Samsung brands.
Video cards: Some cards were "bare" as in just in an anti static bag and some were "retail box" as in containing everything. A couple were "in between" meaning they came in the original box, but were missing stuff. Traditionally I've had probably a 20% DOA rate with the refurb video cards, but lately they've all been good (purchased 6 in the past half year). IIRC all the Sapphire brand cards have come with accessories, but YMMV. I've also gotten one ATI AIW card with everything, but I sweated that one because some of the accessories may be important or worth a lot.
Motherboards: Finally to answer your question. I've had a couple of DOA and a few that failed really soon (days). Most have lasted as long as motherboards tend to last (until caps burst :laugh: ). Probably around a 10% failure rate. Notably, all recent purchases have been 100% functional (knock on wood, about 4 in past 6 months). Also notably, most boards did NOT come with accessories, including a decided lack of ATX I/O shield. I've noticed (similar to video cards) that it tended to follow certain brands. For instance, several Biostar boards all came in original retail box but no accessories. A bunch of Asus boards came in white boxes with no accessories except for one that came in a retail box with all accessories. IMO with refurb motherboards it is extremely likely that you will NOT get the ATX I/O shield. I've probably had about 1/4 come with it. For Asus boards I used to buy from Asusparts.com (sold at eBay). Otherwise I just roll my own from aluminum flashing.