Like others have said, namely Ted and danyalswan, I work much better in a certain state of solitude that enables me to work *without thinking about other people* which generally means that nobody else is home, nobody is outside the house, nobody's calling me (that really throws me off, when I have to stop and pick up the phone).
I'm also my own best friend at the same time, and have gone beyond assuming that it sounds lame or pathetic. The thought doesn't even cross my mind these days. I talk to myself outloud (when nobody is around; if they are, sometimes I mumble under my breath) and entertain myself by coming up with different voices, accents, and even entire personalities.
But as far as real people go, my best friend lives in London and I haven't seen her in the flesh for two years now (though that's about to change, in August), and every now and then I'll strike off a previously-cold relationship with a local pianist, for instance I used to know a guy from a public high school I had the misfortune of attending three or four years ago, and we haven't spoken for several years, but just about a week ago we happened to both be on AIM and, without even missing a beat, we must have talked for three hours about piano and music, and now we're set up to sign up for a Chopin competition together and coach each other on our music. That's generally how things go with me.
Sometimes I feel lonely when I see people, especially those with whom I used to be, or still feel, close to, dating people and spending all their time with them and snuggling up and what have you, and of course I have nobody, not even potentially. But then I remember that, despite that, I have something that sets me apart from all of them, something that fuels me in a different way. I have a connection to music, and they will probably never see it the same way I do. Then, having thought of that, I look at them and think "these are the people who will come to my recitals together and hold hands in the audience while I, all alone on stage where I belong, relax, entertain, and thrill them. Then they will applaud, go home, and make love, and perhaps I will go home, watch a boxing match or Stanley Kubrick video, and fall asleep with my clothes on."
Heh, but really that doesn't affect me a whole lot. More often than not, it actually helps to drive my practice sessions. That said, I do wish I knew how to spark up a more interesting social life, because I run the risk of becoming dried up and boring, and as it is I can hardly talk about anything outside of music.
It's interesting that someone else mentioned his vocal chords atrophying, because I feel exactly the same way sometimes! Talking outloud and singing with my piano has helped me use them more constantly!