I don't know that I'd go as far as couch-surfing, but when you're travelling alone, I think its key to conciously put yourself in situations where you have to interact with lots of people... staying at hostels, or B&B's instead of hotels, taking classes or guided tours. I think those situations go a long way in helping you find someone you may want to travel with in the future.

There are lots of Travel boards with "communities" such as Flyertalk that inevitably have people interested in the same kind of travel as you, where you may find a suitable travel companion or companions. Even if for part of your trip.

My best travel companions other than my sister were found on FT, and I'm sure there are same stories to be heard from the people who frequent ricksteves.com, or frommers, or cruise critic, or the disney boards.