Netbeans is gaining momentum - especially in Java EE 5 space
At least in Germany Netbeans wasn't widely used. In fact I never saw Netbeans in projects. Since 1995 until 2006 I met only one student in my Java EE class, which wanted to use Netbeans instead of Eclipse :-). It was in the pre Netbeans 5.0 days so I prescribed the Eclipse usage...
However, this situation begins to change. Actually most of the students/project participants at least tried netbeans out - and were pleasingly surprised. Especially the visual JSF, Swing (Matisse) editors are very popular. On the other hand the (great for my needs) UML support is almost unknown - which is pity. It is just a single click to install the additional functionality - the diagrams are very PowerPoint compatible - they look really good. In fact I used the UML-module for the documentation of all samples of my book- it saved me a lot of time.
Also the single zip-download gains some additional sympathy. You can start developing Java EE 5 just extracting the jar - and starting the IDE. No additional plugins are required - everything which is needed (for an average "business" project) is already there. There is even one installation with bundled glassfish available. But WebLogic 9/10, JBoss, Tomcat can be also integrated with few clicks as well. Downloading Netbeans you should be carefull with the language support. This drives me crazy. Sometimes automatically the German edition of Netbeans is downloaded, which is fun - but I cannot work with it (even Message Driven Beans are translated into German: "Nachrichtengetriebene Beans").
I'm using the released Netbeans 5.5.1 in my projects/trainings, so the code-editor is beeing criticized, but in Netbeans 6.0 it was totally rewritten and it works really well (however in M10 it is very slow, daily builds are faster, but the stability is dependent on the day of week :-)).
Very important for real world project is the documentation. And the netbeans documentation is really great. Not only online-articles, but also screencasts are very helpful.
However Eclipse's Mylyn is also very interesting...:-)