I recently experienced a problem under warranty with my Compaq netbook. Initially I contacted eBuyer who then referred me to HP support.
HP support responded within 1 day and asked me to perform some more checks, and once these did not resolve my problem they arranged for the netbook to be collected and sent to their repair centre, who are Flextronics.
The courier arrived two days later with a special box and pre-printed labels. I was expecting to wait 2 weeks or more for the netbook to be returned to me, but to my surprise it was returns 6 days after being collected with a new motherboard fitted (according to the sheets included in the box) and not a single mark anywhere on it. I realise that this should be a 'given', but I've dealt with other repair centres in the past (for mobile phones and laptops) and there is usually some scuff or scratch that was not present when it was sent off. As a bonus, there was a coupon for 30% off HP accessories from hp.com.
So, a big thumbs up for both HP and Flextronics (and eBuyer, who called me back the next day after raising an RMA request).