Different types of alone. I've been lucky enough that for most of my IT career I've worked in an office by myself. When I needed a break or just socialize it was all right outside the door, but I definitely like not having immediate distractions. I share an office now and mostly that works fine, but the weeks when we have an external instructor here with a class feels a little overwhelming - noise, interruptions, etc.

Working totally alone (as Steve mainly does) is challenging and I definitely struggled with it. I deliberately scheduled social time into my day - mainly lunches - just to get out of the office and feel connected to the world. It's not just the social part, it's nice to have someone around to bounce ideas off of.

I think most people under estimate the stress that task switching adds, and how much it distracts from work. Working alone doesn't eliminate that (you can easily find other bad habits to make up for being alone...IM, twitter, etc, etc) but can reduce it a lot.