Living the dream
When I was 23, I decided a good ambition would be to visit at least one country for every year of my life. So, if I lived to 70, I would have visited 70 countries. Well, I have now well exceeded the goal (49 in 30 years), but it's always good to have a few in the bank, especially when "boring" things like families and mortgages will presumably come into the equation down the line and slow me down! My total includes several locations from my childhood, but they're still valid!
UPDATE APRIL 2008: Moved to Thailand. It's been an ambition to live and work abroad for a long time now - this is the next level up from travelling. So now I live and work in Bangkok and am seeing more than a tourist or backpacker could hope to.