I hate when people use it every 2 mins... though I use it sometimes, because I don't know how to say I find something funny in other terms... obviously, there are smileys in forums and chat log, but does someone really like Skype smileys, for example ? ^_^
But yeah, I use it when I really find something funny (I mean "mentally" funny, which makes me smile or so, I rarely "laugh out loud" when i'm on the pc), not to say "okay, cool, it was a joke, I have to say I laugh even if I don't".
Also, I use a lot of "weird"smileys, but they are not expressive enough to say I really found it was funny, so I still using "lol".