Just recieved an email from youtube (supposedly) saying that one of my vids has had a loto f hits and that they will pay me if I sign up for each time someone views the vid. They attach little ads and its them that pay me!
Anyone else had this or is it a scam?

sounds scamtastic to me, unless any links in the Email really go back to youtube and not a site skinned to look like it.

Well I clicked on the link and it went to Youtube and followed the thread. Seems its genuine! I will have to see how many more hits I have to get before they pay me though. The minimum threshold before they pay is £60.
The vid has had 58,000 hits so I might start posting it on forums to raise those figures up and get paid!!

It is legit, but there's a pretty major downside that they use a zero-tolerance deletion policy for any suspected copyright infringement, even fully credited tracks etc. This includes soundtracks. I decided not to sign up because of that.