I started using Ubuntu just a few days after WartyWarthog was released. My first impression wasn't that good but after a few days the upgrades looked promising and I decided to stay. Before Ubuntu I had Fedora Core and OpenBSD but in the last months I got dissapointed with both: after experiencing a brutal bug with the former (the Final Release decided to reconfigure our HD geometry) I realized that by keeping it in my machine I was doomed to be an eternal Red Hat beta tester. On the other hand, OpenBSD is great but I was spending too many hours a month trying to adapt it to my needs instead of working toward my own goals. Don't get me wrong, both products are good, is just that the bugs or problems I was facing as a user are not the bugs or problems that spark my interest as a developer.
Ubuntu looks promising. It has the right priorities as a distribution, great community values, a decent pool of talented developers and good financial backup. All those factors are equally important to me so I am planning to stay here for a while.