I mostly smoke alone because I spend the majority of my time alone, and I'm a fairly solitary person. Plus, I have trouble keeping with my weed budget when I'm always hanging out with people. When I'm alone I'll usually smoke one bowl, but with other people I'll smoke 5 or 6 bowls or several joints or blunts.
But whenever I hang out with friends I smoke too, pretty much without any exception. I've often had the experience that was already mentioned where you smoke with someone and then have nothing to talk about and just sit there awkwardly. Happens more to me sober though, weed is a pretty good social drug I think, it tends to make everyone more chilled out and silly which is good for hanging out with friends.
Weed is a great drug for nearly all occasions, I pretty much stay stoned. I find it enhances almost any situation, and I'm highly psychologically dependent. It just depends on what you like to do though.