Friends, as I see it, was the biggest(and I'm not saying best) sitcom created. Shows in comparasion now can't even catch up. The comedy is derived from a situation that the characters find themselves in and the fact they are so different and so easy to 'get' and like, you can partly guess how it will end and still find it funny. They have catchphrase, that even today people still know well. It just works for what it is.
Speaking of using curse words, it works only when used at the correct time. I've seen some shows where they use it a lot and well... it's like watching 10 year olds speak. I personally don't like Everyone Loves Raymond, nor Coupling(funnily enough, I was sitting yesterday about sitting down and trying to get into it). British comedies seem to have fallen to the same problem America has at the moment. Simple slapstick stuff that is in no way groundbreaking.
I watched loads of The Fast Show the other day. I forgot how greatly funny that was.