I've been working purely from home for the last 3 years now, where my clients have all been in other countries. I'm not an intensely social person but about 2 years in I had a period where I did feel really isolated.

In my case, though, I solved this by getting out to twitter/tech meetups and other activies (e.g. I'm speaking at a conference in Amsterdam in June). This occasional socialization is enough for me, though your mileage may vary. Also, it might help that I work in a very social open-source field where I can have continuous contact with other developers and community members.

I must admit, I would hate to go back to regular commuting. In my previous life I only had a 40 minute total commute but even 40 minutes is really valuable nowadays!