I've just spent the weekend watching seasons 1 and 3, and this is about the funniest show that I've ever seen. People compare it to Friends (the only real similarity is that there are 6 people involved, Coupling, however, is actually really funny instead of kinda funny.) but I'd say the show reminds me of Seinfeld, or Arrested Development in the sense that a variety of completely separate plots come together in an unexpected way in the end. It's flawless in its execution. Jeff really steals the show for me. I'd give a list of suggested episodes, but that list would essentially be a list of the entire running.
My sides are still sore from laughing so hard. If you live in America, you can either get it on BBC America or get the DVD's. And you should. Seriously.