Happened to me twice; once at the bottom of a big hill at high speed, which was a bit exciting -- cog unscrewed as I was trying to slow down before some traffic lights, chain came off, back wheel locked up and I skidded to a stop cursing a lot. Second time was just because I was trying to slow down a bit too hard. No damage to me/bike either time, but it left me very wary indeed.

This was using blue loctite and no lockring -- I'm really not a heavy rider, so I reckon that version just isn't strong enough. Red loctite is much better, no problems with that except that you need to use a blowlamp to melt it if you ever need to take the cog off to fix broken spokes or whatever.

-- dan