stilltortoise, sounds like you just aren't interested in the game of discovery if you can't find any…
Couldn't be further from the truth, which was why I asked the question. I've ridden Walna Scar for example. It was great fun, yes, but there wasn't another great fun section straight after it, and then another straight after that. I'm not even saying all trail centres are better than natural stuff, but the Glentress red does seem to be one great section after another without any "filler". How many natural rides can claim that?
Last time I was up in Scotland I rode Mabie one day and then something up in the Lowther hills on the other day. The Lowther hills ride was fantastic, particularly the singletrack down Enterkin burn – and on balance was the better of the two rides – but whipping round Mabie without having to stop and check maps, keeping my heart rate up and having fun on every pedal stroke was just a different kind of fun entirely.
Now give me a big wilderness ride with as much quality and fun singletrack as you get at a good trail centre, and I'll be a very happy chappy…I don't even mind looking at the map!