Groovy in Action has been out for a while now. Is it still 100% relevant? If not, are there any references sites that give the differences between what's in the book and what's in the latest release? Will there be a second edition? Perhaps to coincide with Groovy 2.0?
Everything in Groovy in Action is still 100% relevant.
There have been a lot of improvements to Groovy since the book came out but the concepts have not changed and the developers have been very careful not to break old code. This will remain true for all Groovy versions labeled 1.x.
It is still a long way to go until Groovy 2.0 (probably a year or so but don't take my word for it). Groovy 2.0 will have new concepts and is likely to break 1.x code. My intention is to have a second edition for Gina for Groovy 2.0 but not before.