The pot smoking community is heavily based on friendliness and the "it's all good" mentality. It's very common for smokers to smoke people up, despite the expensive cost of weed.
I myself am always ready to smoke anyone up, and will always go out of my way to find someone to smoke with. Smoking is always funner with people, and pot's a very social drug.
I've developed relationships with people I call smoking partners. These are people you smoke with a lot. Few people have pot all the time, and in this way we're always there to hook each other up. When my friends are low on nugs they know I'll be glad to smoke them up, and vice versa.
Generocity rarely goes unrewarded, and it's always good to have friends you can smoke with so no one goes sober for too long ;]