I know this post of a few weeks old, but just thought I'd post my experience today (Monday).
Brought my Dell 2407WFP on the 9th June 2007 from Overclockers with a  4 year warranty.
Made a note of the work order etc.  Have never registered my monitor with Dell.
Today I phoned up Dell, initially got through to India who asked for my service tag, as soon as I said it was a monitor and I don't have a tag they transfered me to their monitor department which was in Scotland.
The guy asked for the serial no (20 digit no on the back of the monitor) and from that found the work order etc himself. He asked where I brought it and when (I presume to check I was the original purchaser), he asked what the fault was, and apologised that as I phoned up after 4:30 I wouldn't get my replacement tomorrow, I would have to wait until Wednesday instead.
I double checked with him that my 4 year warranty would still be valid on the replacement monitor (different serial no etc), and he confirmed this (although I have made a note of my original serial no, just in case any dispute occurs should a fault appear in months to come).
He made it clear I would be receiving a refurbished monitor which after 10 months of use, I would expect (and as long as it works, I'm happy)
All in all a first class service, I'm very pleased.