[mjn]

In my case it's depended a lot on the other person. My closest friends fall into any combination of: 1) people I talk to mainly in person; 2) people I talk to mainly online; and 3) people I talk to frequently through both mediums. I don't see a strong inherent difference between the three categories, at least in my case; my mostly-in-person-chat friends aren't generally closer friends than the other categories. But with some people it's very hard to build more-online friendships, mostly people who, either through unfamiliarity or inclination, don't use IM or IRC in a conversational way with nuances, and treat it instead as more of a stiff/impersonal medium. With other people it's the reverse, and actually hard to build more-in-person friendships, especially with people who are much more open in text discussions than in person (common among tech people, including myself).