These days it is pretty safe to say that Java developers are generally divided into two main camps when talking about their IDEs. There’s IntelliJ IDEA which is a commercial product from Jetbrains and there’s Eclipse which is a free open source product.
Personally, I think both products are good for the Java community. They both offer amazing features that improve developer productivity, are easy to work with and provide plugins to extend the base product offering. What other programming language can even say they have a comparable IDE? If interested, check out this link about the recent Visual Studio 2005 concerns.
I generally agree with what Tim says, that because IntelliJ IDEA relies on sales to make money, that “quality, ease of use and completeness of the product” are key considerations. Yeah, the latest 5.x releases have had their share of issues but if you look at the product as a whole, it rocks! Develop with pleasure!