I bought RubyMine when it was first released and recently paid for upgrading to version 3.0. I switch between using TextMate (or GEdit on Linux) and RubyMine for both Ruby and for Rails development but since getting version 3.0 I spend almost all of my time using RubyMine.
Rails 3 support is very good and working with RVM is a nice new feature. I never used to use the Ruby debugger (at all!) but I have used it twice briefly in version 3.0. At least for Rails 3 development I still separately run both rails server and rails console outside of the IDE – a matter of personal preference.
I was using PyCharm (also by JetBrains) a lot for 2 weeks and the autocompletion hints and instant syntax warnings really helped me because my Python and Django skills are light-weight. I don’t much need autocompletion hints and instant syntax warnings for Ruby and Rails development but it is unobtrusive and often useful.
EDIT: Since I wrote this blog I have started using the Model Dependence Diagram fairly often. It would be great to also have an option to show a UML class diagram.
My only real disappointment with version 3.0 is that it does not implement the tear-off editing tabs (i.e., tear-off to create a new and separate window) that the latest version of IntelliJ supports.
That said, using RubyMine is a comfortable experience and the IDE features stay out of my way until I need them.