i've owned two m8s and currently own and frequently use an x-pro. i was, with some sense of sadness, glad to get rid of my m8 both times. i absolutely love the x-pro.
if you've done any reading at all, which i'm sure you have, then you already know what sort of images you'll be expecting from the camera. and ken rockwell says the x-pro is better built and produces better images than his m9, so you know that's true. the images that come off the pro are just stupid good. it's small, light, well built, 100% ergonomically sensible, very easy to use but not in a way that makes it feel like a point-and-shoot on steroids, seeing images displayed in the evf is absolutely AWESOME, etc., etc. the only downside that i could possibly see with having a pro instead of an m8 is the range of lenses. you know what's available to you if you buy an m-mount camera, both selection and price-wise. meanwhile, there are only three lenses currently available from fuji. sure, you could get an m-mount adapter, but ehhh... i would never buy an m glass for the x-pro. cost. although i use old nikkor lenses on my x-pro and it's quite pleasurable. i've even considered by more manual nikkor lenses for the x-pro, which is funny because i never considered doing that for my nikon dslr. besides, the fuji x-mount lens selection will surely being to grow, and the ones that are offered now cover quite a nice range and are quite good to excellent in my opinion.
i guess what i'm trying to say is that, if someone just offered to give me, free of charge, either the x-pro or an m8/m8.2, i would without hesitation pick the x-pro over the leica even when considering value.