I recently switched from IntelliJ to Eclipse. I'm still an IntelliJ fan however. One of the things I like about Eclipse is it's support for Maven (which I'm also a big fan of). Does IntelliJ provide Maven support and if so, how well does it stack up against the support provided by Eclipse.
I have always preferred having an agnostic build tool like Ant or Maven as the basis for our build environment and then developers can choose whichever IDE best suits their particular needs. Personally, I was very fond of IntelliJ (having switched over from JBuilder).
After having used Maven and adopted the Maven project structure, life-cycle and separations of concerns philosophy, I would have trouble going back however.