I think it makes a *huge* difference whether you're single or not... not because you're always spading if you're single (altho some of us do), but because if you're in a relationship, you know you've always got someone to go home to and hang out with...
The thing with London is if you don't meet new people, you will get lonely *very* quickly... there's a few reasons for this... for a start, people don't stay in London for long, so you get used to people leaving all the time... also, on any given weekend, half you mates could be out of the country, the other half doing something you don't want to do (e.g. going to a club you're not interested in). It pays to keep meeting new people, so you always have people to hang out with.. I've met probably about as many people in the last 3 years as I have the last 7, 8, 9 years in NZ.
Besides that, London's what you make of it. If you don't go out, do new things, take some 'social risks' (e.g. turning up to a party by yourself where you know hardly anyone), you just won't enjoy the experience as much. On the positive side of people leaving, and it being a big city, you know there are *always* new people to meet, and new places to go.
As far as the stereo-typing thing, I'm sure it's been a factor for me at times, but you can break those down pretty quickly (with most people anyway), so long as you don't let it get too much into your headspace.
So basically, no, I can't really relate to what you're talking about at all.. but I guess a place like London is going to be different for everyone...