Looking at the javadoc for the Groovy enhanced java.lang.Object there are some typos.
From the dist docs 1.5.1 open the docs (/docs/html/groovy-jdk/index.html) and click on java.lang.Object.
It list all the new methods we have (they are fab BTW)
However there are a few typos and some JDK1.5 printf methods that are not in the summary.
I have attached a patch for it. It was from the SVN from the trunk.