I just punted mine yesterday through O2 recycle.
Sent it yesterday special delivery @ 2.30pm and got a text at 11.15am this morning saying they had received it and that I should have my cheque in a couple of days £70.10.
Yeah you might get a tenner more on ebay but really is it worth the hassle.
I could have kept it as a back up phone as I really loved my desire it was like an old friend. But seriously once you get your hands on the one X you realise how much better it is and you soon forget about the old desire, it is like night and day.