Jester is seeing a little action nowadays. The Google Code Blog has a post today about Google Gears on Rails, a Rails plugin by Michael Marcus and Rui Ma, that extends Jester to wrap over Google Gears. It effectively lets your controllers read and write directly to your users' machines, so they can use your app offline. Check out the install and usage instructions for details, and listen to the Google Developer Podcast episode where the authors are interviewed.
Nat Budin also just announced that he used Jester to build an in-place-editor plugin called JIPE. He's built some pretty cool Rails helpers for in-place editing that are more sophisticated than what Rails offers by default. Check out the README for install/usage instructions, it's pretty easy.
These two projects are great evidence that Jester makes for a great supporting library, something easily built on and extended. Rails' REST conventions are powerful stuff, and I hope people keep thinking of more ways to prove that.