I'm using nant for OpenPetra.org.
Before I used ant for a big commerical Java-Project.
What I'm missing most, is the macrodef task, which is available in ant. See http://ant.apache.org/manual/Tasks/macrodef.html for more information.
Mainly it allows to execute more then one task with similar configuration. This is helpful for more complex things and complement the PreSetDef from ant.