Just tried this IDE for Ruby, I was having problem to install the plugin into Eclipse 3.2, then switched to new 3.4, everything works OK.
I have no experience on NetBeans, but some people said RaDRails is quicker, intelligent and easy to use. This the intelligence I got. But I tried to use it as an online help, it seems not all the methods can pop-up after the dot.
Later I realize I can use the build-in “Ruby Interactive (RI)” or “Ruby Core API” view.
Here is a poll showing RadRails is 3 times popular than NetBeans.