I was wondering how to keep track of how many builds have taken place, putting it together into a overall product version number with the Subversion Revision number. It turns out that ANT actually keeps a record of builds itself using the Buildnumber task, all you have to do is produce a blank build.number file. If the build.number file is local to the build.xml you need no special attributes, ANT will update the build number for you.
How good is that? Marvellous I think is the word you need.