I won't add back people who add me to their friends list unless I've actually communicated with them. I've had some people add me without me even recognising them and I'd rather they actually contact me if they want to get onto my list than just do it for the hell of it.

For the main topic at hand, I find it extremely easy to make friends online and rather difficult to make friends offline. The biggest problems for me with making offline friends are that I don't like to mix work life with personal life (hence, I don't hang out with work colleagues after hours) and the fact that I'm still probably four years younger than anyone else at work, so it's just a bit weird. I like to think I get along with pretty much anyone I want to get along with, though, so it's not a problem for me when I meet new people. I just don't make a lengthy habit of meeting them because it's very rare that I want someone who I know in the real world to know me that deeply, especially when they're generally that much different to my preferred friend-personality-type. I prefer open people who, er, don't know the rest of my work colleagues. People at work always have a tendency to gossip and I don't like that.