Yes you can run Ant without Eclipse. What I meant was, that we have launch configurations to run our build scripts out of Eclipse.
While that doesn't tie us to Eclipse, the plugins we use do. That includes a custom one that belongs to our framework to generate components.

We do have a custom environment after all, just not a lightweight one. But there's either a full blown IDE or just an editor. Eclipse has it's own Java parser so it actually understands what you are doing. It knows exactly what kind of instance/object you're trying to call a method on and provides suggestions. It can, for example, instantly show you all inheriting classes of the current class or all classes that call a certain method of a certain interface. The list is endless :P

The real time warnings/errors as you type are very helpful, too. Imagine having a build time of ~15 minutes for the whole project (server+client+deploy to JBoss) on a Core i7 + SSD and it fails half way through because you somehow forgot a semicolon :P