I joined a new campaign at my local gaming store this weekend; we're playing A Song of Ice and Fire, the RPG of George R. R. Martin's Westeros fantasy setting. And even though we played for barely 2.5 hours, it was a substantive session—we got more done in 2.5 hours than my current group gets done in 5 hours.
Paradoxically, one reason why we got so much done is because none of us are friends. I mean, we're jovial and polite around the table, but we don't gossip about girlfriends or the latest movie we just saw, and we don't go off on crazy tangents about unrelated stuff. Now, these things are the staples of many a game group, and truth be told I wouldn't want to go without them—but this session was a really interesting glimpse at what can get done when the group focuses solely on the task of gaming.