I've offered someone three quarters of what I paid for my second 4870X2 (£200 from £277), the new alternatives are worth much more, but this is in line with what others on ebay are charging. £77 isn't too much to lose for 7 months use I suppose... :S
Selling since I will find it much more difficult to sell when the 5870s become really prominent, and I can live with a single X2 over christmas, but will NEED to sell them in order to afford a 5970.