Went to Drunlanrig castle yesterday, I must say the singletrack there is bloomin' brilliant! Quite rooty, but it was dry so not probs there, and flows really naturally, not looking manmade at all.
With the sun out, it was positively idillic in places, swooping through the trees. You hardly ever notice if you are heading uphill or down overall, just concentrating on the brilliant trail!
Overall, a hidden gem! go there!
(sorry i didn't take any pics )
Edit: Talked to Rik Allsop too, great bloke and evidently a great trail builder.)