I've been watching Ruby on Rails for a while now. It seems to be gaining some momentum.
Ruby seems like a nice language, and the Rails framework appears to add some WebObjects-like functionality. It looks like it's got some stuff that approaches Direct-to-web. It still doesn't look quite as elegant as WebObjects, but it is definitely interesting, and tries to be pretty cleanly MVC, which is nice. It's also just sitting there at /usr/bin/ruby begging to be dusted off and called into action...
Basecamp was the first "real" app that used Ruby on Rails (and it's a beauty app, to be sure). I'm sure there will be some others going live Real Soon Now.
I'd be interested in developing an app using it, except I'd have to throw away all of the java libraries I'm using (including APOLLO and PXFoundation). When/if I get a chance, I'll work up a simple app to act as an alternate front end to the Asset Management Database, to see how well it works.
I've also been rolling around the idea of building more stuff in PHP, but haven't found a decent framework to use, and I really dread having to roll everything from scratch. To be fair, I haven't really looked very hard, either...
Update: MacOSX 10.3 ships with Ruby v. 1.6.8. The latest version is 1.8.1 (downloadable here).
Update: ImageMagick is available in Ruby via RMagick - there's one dependency I don't have to worry about...
Update: A Slashdot article comparing Ruby on Rails to Java Spring/Hybernate - sounds promising for RoR