They call it your social life for a reason.
I for one love not being constantly yipped at while deep in though about what I'm being paid to do, then going and doing what I want, when I want, with people I actually like.
I think you need all the different elements in your life, but it is often most effective to combine different needs together (such as socializing with work friends or helping social friends with a work project). It offers opportunities to make more meaningful friendships and a better work environment.
Then I turn off the skype chat and knock out a iPhone app when it's time to stop chit chatting.
I also help setup NSLunches in Atlanta with other iOS people and setup lunches around town with various other folks.
I think the typical startup lifestyle changes this a bit, though. We who run startups( generally )don't work 40 hour weeks, and if you're even a bit extroverted, chances are you're going to need to "get energy" from social interaction with your coworkers, since time to do this outside the office is fairly limited.
With the standard introvert archetype, this is likely a non-issue. My money is on samtp being an extrovert, and you( and I )not capable of empathizing with the odd need they have for such interaction.
I just don't find the pleasure of talking with someone compatible with parts of my job. The other parts it works wonderfully with.
You think long hours are unique to the startup world? You can have a social life and work long hours. You just have to intentionally do it. IMO its a sign of maturity and adulthood.