Today is the 2 year anniversary of the release of jQuery (celebrated with the release of the excellent jQuery 1.2.2).
I remember doing the first release at BarCamp NYC (combined with the mention of two other projects of mine that fizzled: Feed Pile and Idea Shrub). While I had released a bunch of open source code in the past, this was the first one that I put some serious effort into getting publicity. Luckily it made it onto del.icio.us/popular, digg – and the rest is history.
Amusingly, the entire chain of popularity was due to the fact that I made a troll-y comment on a Prototype blog post (when they announced their new selector feature) and it was discovered and re-blogged by Ben Nolan (creator of the Behaviour library for Prototype). From there it hit the Rails community and was launched onto del.icio.us, digg, etc.