I downloaded the spanking new Ant 1.7.0 yesterday. And it failed on the first build.xml I tried it on.
I have many little build.xml snippets in my ~/temp/src/ant directory. The antdtd has is the first one listed. When I ran it, Ant 1.7.0 complained that a certain class related to the ftp task is not present and aborted. I haven't checked the mailing list archives or the documentation yet, so I don't know the full story.
I have switched back to Ant 1.6.5 for the moment as it looks like switching to Ant 1.7.0 is not going to be a trivial task.