Yeah, whoever said 80% left or right i reckon is onto something especially if you're using lots of reverb 'cause it makes the reverb sound more natural to be wider than the track.

probably more important to keep your constant driving stuff within this 80% kind of bracket

on the other hand, pads you can pan outside the speakers a little with some stereo expansion if you choose to use them and some special effects work wonders with a bit of this too.

and if you were going for a drier mix I don't see why you shouldn't use all the available space, sometimes it's fun.

(I mixed an acoustic album for someone recently and by the time they'd dropped the last track down they must have been well pissed and their usually excellent timing had gone a bit so I stuck the lead vocal on the left speaker and the restof the band on the right speaker till half way through and filtered the lead vocal to be tiny. the band seemed dead cuffed with it and it's really quite enjoyable to listen to ... not that you could do that with must dance music but it illustrates the point)

An awful lot of dance music is mixed in what someone once described as "big mono" where most of the sounds are pretty much down the middle or just smeared with pitch or delay tricks across the stereo field. Makes things sound posh quite quickly but gets a bit boring...