Most of the time I run alone, and I rather enjoy it. Heading out early before the sun and most of the city is up and buzzing is a quiet time between me, the cement, and my run. Don't get me wrong, I love running with friends and catching up, but I consider those times a little treat.
During a run my mind can process nearly everything with more clarity. When I was taking classes I used to work through possible exam questions in my head, sometimes I think of unanswerable questions I've encountered in the lab, contemplate ways to make myself a better all around person, or just sort through things I'm generally frustrated about.
As a child I attended therapy sessions to aid in the healing process of my parents divorce. The one thing that stuck with me for all these years is to do something physical to exert the frustrated energy, and as I've aged running has been the outlet of choice.
I relish the alone time and the mental quietness.