I went for drinks at Sketch with some friends, and had quite a good time despite myself. The place is, to some degree, something of a contradiction.
On the one hand you're pleasantly surprised that there is no cover charge or smarmy doormen. On the other, the decor and design of the place makes it very obvious that Sketch has a high estimation of itself. Personally I was a little put off by some o the bizarre sculptures, although I am quite certain that they were very deliberately chosen - for whatever effect.
Again, while on the one hand prices are quite high and, at least in my experience, service a bit spotty (the feeling I got was that if the waiters are cool enough to be working at this hip club, they must be too cool to serve you), there is a surprisingly relaxed vibe about the place and I genuinely enjoyed sitting in the bar for an hour or so.
Clearly the place is much bigger than I first realized - there are two dining rooms and a very peculiar (but fun looking) round bar at the back, as well as the main bar in the front of the club. As Adrian wrote, the toilets are quite a different experience, and worth a look even if you don't need to use them.
So in the end, I was quite pleased with Sketch. It's atmospheric and proffers great people-watching. Still, it can break the bank, so I wouldn't necessarily spend the night there - maybe just grab a drink or two after dinner like we did.