In and on and 'a'
How to sound smart when talking about the Internet:
You don't have 'a facebook.' Facebook is a place, a network, not a page. You're 'on facebook,' or you 'use facebook.'
'Friend' is a verb. "I'll friend you," is a totally valid thing to say.
You don't look up things on 'the google'. It's just Google, no 'the.' 'Google' is also a verb, as in, 'Google me'.
Instant messaging refers to a wide range of software tools and communication channels. It's called 'IM' and it too is a verb.
A blog is something you have (unlike a Facebook). And blog is also a verb. As in, "I have a blog, this blog, which you probably found by googling me. I blogged about Facebook (which I'm on but don't use often). I don't IM, and I'm impossibly lax about friending people."
[Jackson chimes in that a blog is the whole, and that a post is just one article (like the one you're reading). So you don't say, "I wrote a blog about that," you say, "I just blogged about that," or "did you read my post on how to talk about the Internet?"]