Danno first "deprecated" static SwingBuilder.build(Closure) and has now introduced some crazy Groovy metaprogramming code into SwingBuilder as a "workaround" to the bugs caused by his attempts to make SwingBuilder threadsafe (which shouldn't be done and is a major and trouble plagued issue with no JIRA).
static SwingBuilder.build(Closure) was introduced (by me) in Groovy 1.5 and is what I consider the preferred method for using SwingBuilder. It specifically addresses the common case of a user wanting a Swing UI with the minimum code and correct behavior wrt. EDT without having to even know there is one.
It has been in use for more than a year now and is clearly being used by Groovy folks:
and many more...