Sorry for the delay in reply ... I forget which threads I reply to some days!
I've not been there yet (waiting for the weather to stablize a bit more) but a lot of people advocate anything below Aysgarth Falls as being a "prime" stretch. Czech nymphs and North Country spiders seem to be the favoured tactics. Heavy grayling population and good trout numbers too.
I'll let you know how it goes when I get my line wetted down there
UPDATE: Managed to pop over there yesterday afternoon. Didn't get any action myself but a chap who was just leaving as I came had 3 trout on worm over the course of the morning. Saw three rises but neither nymph or dry was interesting enough to cause a take.
Overall it looked like a nice river, typically peat stained but with a lot of features plus fairly contrasting fast and slow flows within short distances. I think a trip back in 3 or 4 weeks would be more entertaining (and warmer!)