I'm not a big comedy person, and am not in love with Alyson Hannigan, so I haven't bothered watching How I Met Your Mother, but having watch it tonight, I've gotta say it's a solidly written show. Witty (select lines behind cut). Believable characters -- frustrating, but realistic.
five-year old (?) boy: "Are you a lesbian?"
Robin: "No. Are you?"
Barney (to one of the small children): "Tiny five."
Lily: "It's my best and most annoying trait." [being right]
Marshall: "You just got burned - phonics style."