Debuttonizer is no longer available.
With the arrival of Mac OS X 10.5 (Leopard), it's clear that the "new-fangled" look of Mail.app's toolbar is here to stay; even Preview.app sports the same look.

So, I think it's time to retire this little hack. Happy? Sad? Ambivalent? Drop me a line: mail-debuttonizer (atmark) 512k.org.