Steve tried to warn me, but I was, like... hopeful.
Turns out Aptana is basically Eclipse in disguise, and although some of the stuff that drives me nuts about Eclipse has been shaved off you can still see its heritage.
Why, java people... why in the name of all that is holy can't any of your tools "import" a directory that's already in the project target space? Other things it lost points for: the code view areas for HTML, js, and CSS files were whited out (ie, no text showing up) until I previewed the document, preview freaked out a couple of times, and the nasty editor habit of dropping ".tmp*~" files all over the workspace.
The insanely awesome good stuff: the CSS and js editors supports intellisense like code completion AND error highlighting. Strip the rails support out, and that alone is enough reason to keep it on the hard drive. CSS is my kryptonite, but Aptana just handles it beautifully.
I've decided to check out jEdit and NetBeans as well.
jEdit's got some nifty plugins that enable it to do stuff like editting files over SFTP, SVN integration, theming, but at the end of the day it's more of a text editor than an IDE. Still, it has potential to replace the trusty vim on Linux and notepad++ on Windows.
NetBeans offers up a Ruby-only install that seems extremely well integrated into Rails development. It even went so far as to call the rails command to setup the project and ferret out the database info the db.yml file up front. It's also sporting code completion for JS, so... I'm feeling hopeful about it (despite Steve also warning me about this one, too).