I describe my case, maybe it would be helpful for someone.
PURCHASE
I've bought OcUK B-grade motherboard (Asus P5N-T) and have tested it 3 months later. It was not stupid as I've bought it for further resale, so I couldn't check it during that 3 months, BTW I was using AMD platform and such checkout was impossible. Mobo was highly unstable even after my treatments, so I decided to RMA it.
WARRANTY
OcUK sells B-grade stuff as (for example) "14 days + Any additional balance of warranty remaining with the vendor of this product", so I thought they are responsible for the whole replacement procedure. No way. They are responsible within 14 days and then it's customer's matter: where, how and how much. IMHO their warranty description is a bit misleading, because '+' sign means addition to something, so if warranty in OcUK is "something", this plus gives more to *that* something - it's just logical issue. Correct warranty description should contain info: who is responsible for first 14 days *independently* on the whole *vendor's warranty*. I'd say roughly "In spite of any additional balance of warranty remaining with the vendor of this product, first 14 days is OcUK warranty". Whatever. After 14 days you have to RMA mobo on your own.
WHERE
There's a company in Scotland as I remember. They sell RMA service for 18 pounds. Simply: you buy it and then you are allowed to send them motherboard (*just* mobo, no cables, no additional stuff). Of course, you have to pay for 2nd class parcel (about 6 quids), but it's really end of expenses. So when mobo has been sent...
HOW
This 18 pounds guarantees that mobo will be sent to Asus factory (or wherever they can fix it, or replace it) and will be back in some time. Usually - about a month. Brought by a courier, in the same package you've sent it earlier.
SUMMARY
Asus gives 3 years of warranty for their mobos. Even if you don't know when it was produced, just google for release date. So if you've bought B-grade, or used mobo with no warranty - there's still your own RMA (within 3 years from release date). One RMA costs about 24 pounds. Horror starts when after second RMA you still experience bugs....
P.S.
I'll edit my post later, I have to find this company's web page first.