I've been running N since Preview 1. Preview 2 grew increasingly unstable until I did a factory reset which helped considerably. I got Preview 3 yesterday and it seems to be significantly better than Preview 2 but it won't be possible to really pass judgment on it for a couple of weeks. Preview 2 ran pretty well for a couple of weeks before it started to clog up, the symptoms were that thing would slow to a crawl until I killed everything with ES task manager or did a reboot which would fix things for a while. As I said at the beginning a factory reset fixed that problem. Preview 3 feels significantly faster than Preview 2 and hopefully it's more stable. I'm using it as my daily driver but I'm a techy who's comfortable with beta software, if you are comfortable with beta code then go for it but if you want maximum stability stick with M.
UPDATE: I've been running Preview 3 for a couple of days. It seems really solid and the performance is very snappy. I think its ready for wider use, it's not for just the extreme bleeding edge types anymore.