Groovy 2.0 release notes
JDK 7 / Project Coin alignments
Underscores in number literals
Notes to the invokedynamic implementation
The usage of JDK 1.7 before update 2 may cause a major slow down, since there has been an internal synchronization issue in the implementation
In JDK 1.7 update 2 there is a potential internal error appearing if package private classes are used in the call site.
Those are no bugs in Groovy, but bugs in Java