Great command line support - seems to be comfortable and capable on the command line. This one was thing I missed with PHP. Although its definitely command line capable, I wouldn't call PHP "CLI-friendly".
Active user community - seems like everyone and their mom is using ruby!
Good documentation. Nuff said.
YAML - No! I won't buy into it! I'm sticking with XML!
Slow? - Am I doing something wrong? Ruby on Rails seems really slow to me. At first I thought it was webrick (see below), but now I'm running ruby with Apache2 and fastcgi (fcgid) and its still slow....
I just got going with retrospectiva, a software focused ticketing system. It includes a wiki and a blog system, but I prefer Wordpress and MediaWiki for those functions. Thankfully, retrospectiva includes a method to remove those extensions! What I like about retrospectiva is the way it integrates a ticketing system with source code management, similar to Trac. Both of these systems thus have milestones to help track your progress. That in itself is pretty sweet.
I ran into a glitch with retrospectiva because my subversion repository is an amalgamation of different external repositories. Retrospectiva can't access external repositories, so I created a new local one and it worked fine. Besides that, retrospectiva is kind of slow. It could be due to the fact that I was running it on the built in ruby webserver, "webrick". I'll try lighttpd next.
I also got confused trying to find out how to control guest access to the projects. Finally found it under "Groups -> Default". Hope that helps! You can control what the users have access to.
Urg - I'm still troubled by how slow my retrospectiva install is going. I'm trying out trac and its way faster. I think I might just go with trac. Trac is written in python and SQLite is recommended as a storage mechanism for it. So far I really like it. I was concerned that the wiki would be readily hackable, but you can make pages write only.