For those of us in a multi-project, multi-IDE ant-based environment, it seems to me that the answer is straightforward. We don't want NetBeans messing with our production ant files; we can edit them perfectly well with the NetBeans editor (good job!). What we need is a straightforward way to tell NetBeans what LIBRARIES our ant file is using: jars, sources, javadoc. And apparently we don't have that.
The "Java Source Classpath" can be used to declare library jars, but what about source and javadoc? After studying both the dialogs and the project.xml (and hunting around unsuccessfully for the schema or dtd for project.xml), I could not figure out where to put the pointers to the library sources or javadocs. What to do? Pretend it is project source?
This is pretty much a deal-breaker for me -- not just because the individual problem is so serious but because I ran into it 1/2 hour into using NetBeans and because it appears unresolved. I have to assume I will encounter a pile of similar problems down the road.
IDEA works perfectly with an ant-based project; Eclipse appears to be completely lame; NetBeans seems somewhat more like Eclipse than like IDEA in this area. In other areas--like updates/plugin management, PHP editing, footprint-- NB seems superior to Eclipse and comparable to IDEA.