trail running is by far my favourite and I do it much more often than road running, not least because i can take the dog with me!
The thing to remember is not to get too caught up with mins per mile as the terrain alters so much.
I'vecompleted quite a few trail races this year (avebury 8 was most recent) and hoping to work up to the purbeck marathon in september next year!
i'd recommend buying 'Trail Running' magazine, but only for the articles of course, not the pictures of running kit *ahem*