It’s been some time since we’ve seen any new javascript minifiers out there. Google Closure was probably the most recent but many argue that was basically a re-hash of Yahoo’s YUI Compressor.
As web applications get better, there is more Javascript.
Caching has been a big help to this—even though only effective for about 40-60% of your audience. The problem with caching however, is that when a new version of the code is released the user must download all of it again.
Diffable JS makes this less of an issue becuase the user might only need to download 10KB of changes instead of 200KB. It also sticks close to #1 rule of web developement: make browsers download as few files as possible.
I think this project is awesome and I need to spend some time giving this a proper look-over.
Diffable JS: http://www.stevesouders.com/blog/2010/07/09/diffable-only-download-the-deltas