Fuzzy sent a link to this piece on adding continuations to Java, more or less. The article mentions a potential JSR, but from reading through it, I'd expect a good bit of experience should be racked up before that would be practical. Apparently the implementation works now but plays some tricks to do so.
Continuations have been incorporated into several Web application frameworks, including RIFE and WebWork. In this interview with Artima, RIFE project founder Geert Bevin discusses how continuations can simplify complex workflows, and how they are implemented in RIFE.