Any good Urban Fantasy novels or short stories with the Internet as a key theme?

There's a bit of it involved in a paranormal romance, BONDED BY BLOOD by Laurie London. Not the main focus by far, but it does come into play.

I would check out Alma Alexander's World Weavers series: Gift of the Unmage, Cybermage, and Spellspam

It's safe to say the internets are important in my series - the protagonist is a massive geek, explicitly referencing memes, speaking in lolcat (though not constantly, just little bits of "I can has?"), losing hours to kitteh videos, etc.

Tech as a whole is of major importance as half of the main cast are nanite constructs, and have HUDs, in-brain instant messenger/not!Skype, and have to deal with upgrades, widgets, and the occasional OS glitch. ^_^

Lauren Beukes' Moxyland might have some of the things you're looking for, although I think that's categorized as "cyberpunk," rather than "urban fantasy."