Being social does not automatically make one a team-player...sometimes being social is an illusion to make up for some apparent deficits. I think actions still speak louder than words.

I've seen a lot of mediocre work (given, some people are at different stages of experience/talent too)...but some managers overlook it in favour of having best friends and fun times at work...but they won't tolerate the opposite: great work but less social time.