IDEA can do everything that eclipse can... only better !
Eclipse cannot do everything IDEA can.
Comment from another yet unknown software developer to the above line:
Can IDEA be used for free?
No, but in the real world, the TCO for licenses is minor (VERY minor) compared with the productivity gained by professional tools.
And for specific use (qualifying open source projects and JUGs for example) free or discounted licenses are available on request.
Can IDEA lay open its source?
The source code for the OpenAPI (which is used for building plugins) is given and distributed for free.
Can IDEA be enhanced/modified freely by anyone on basis of IDEAs source code ?
Why would you want to do that? To build another IDE??
Can IDEA do multiple perspectives and views?
Not at the moment. Personally, I don't find it useful either. There's a "Favorites" view but I don't use it. I prefer to see it all
Update: 6.0 and 7.0 introduce something of the kind, but more useful than Eclipse's idea.
Can IDEA keep all java resources compiled in background?
No, nor would I want it to.
Can IDEA show differences between local archives (zip, rar, jat, etc.) and the versions checked into CVS?
Can IDEA do the JBossIDE?
Question is, can JBossIDE do IDEA?
Can IDEA startup quick?
Quicker than Eclipse, for sure.