Met quite a few people from here, though most of my fellow Brits don't really post here anymore. Some random comments:
XJDenton (aka Squibby) - pretty similar to his posting style, just a bit chattier. Incredibly pleasant chap, very intelligent and witty.
Rumborak - Pretty similar to his posting style, again intelligent and witty, but in person has the main benefit of being more relaxed and not trying to wind people up!
Sigz - really awesome guy! He spent a year in London studying at Imperial College which was amazing as I got to see him quite a lot. Definitely very similar to his online persona - intelligent but a lot of fun as well.
Nick - basically exactly as I expected, but then I know him really well even though I hadn't met him before this summer. Was a very cool experience though, great to spend the day with him and Mrs Nick.
Millahhhhhhhhhhh - Really interesting guy, always found him respectful and intelligent on here but he was definitely a lot more talkative in person and really fun to chat to.
Jingle - similar to Nick, I feel like I knew him pretty well so I think he was basically what I expected. We had a really nice day visiting him and his family - especially enhanced by BBQ and cake!
A whole load of others but these come to mind right now. Will post more.
EDIT: Of course Arch Benemy, nightmare_cinema and AcidRainLTE I've met a fair few times - all really cool people as well!
EDIT 2: And of course I'm good friends with TimmyHiggy, but I knew him in person first and introduced him to DTF, so that doesn't really count.