I think a lot of it's down to setting. For example, in the UK, if you're into D'n'B raves, you have to be carefull who you start rapping with, particularly in Birmingham or Nottingham, where I often go out. A lot of the time, it's best to stick with your mates and stear clear of the rude boy types that show up at those raves. That said, I have had some awesome conversations at said raves with people from completely the other side of the tracks via the medium of e. I remember chatting with a Yardie geezer on crutches once at a rave in Brum for hours, him telling me about why some "manz dem bruk him up" and chatting to me about music in general. Proper random.
At breaks nights, people think they're too cool to chat to randoms. Ditto any sort of "haircut house". Hard house/hardcore/techno etc raves are usually full of random chatting opportunities, although I often get the impression that that's because people at those events feel they have to do that to prove a point.
Personally, I'll never just chat to a stranger completely out of the blue any more. When I'm on the dancefloor I tend to become sort of hypnotized and let my mind wander and find it hard to talk to my friends let alone anyone else. However, when I go and get a drink or sit down with a cigarette I'll quite often chat to random people whilst there, and find it easier to do so than normal. Plus there's all the obligatory little bits of contact with randoms: passing spliffs, cigarettes, gum, cuffing hands in mutual recognition of a big tune, spotting people you always see at that particular rave, etc
As a youngster, I would gushingly chat to randoms or, worse, people I half knew but, once I was more familiar with the drug and started to be on the receiving end of this, I realized how annoying it is and modified my behaviour. Things like repeating yourself constantly, constantly asking the same question over and over again, forgetting what you're saying half way through a sentence, completely zoning out while the other person is speaking and generally being far too nice are not a good luck, however amazing and "spiritual" you think they are initially (My own little party trick used to be starting to skin up, forgetting half way through, then starting again. I'd leave little trails of open skins laced with baccy and skunk everywhere I went)
On a side note, relationships/friendships forged on e can often lead to disaster. Things seem different in the morning. There's always that little moment where the feeling's suddenly gone and you just want your own space and familiarity. If you just swapped numbers with someone it ain't too bad and you may subsequently realize you actually do like them. If someone's come back to yours though (or vice versa) or, worse, you've ended up in bed with someone there's that horrible moment of thinking"fuck, what am I doing here?".
Best to keep these things on a down low I feel.