People reading this blog might be forgiven for thinking that I don't do software development for a living, so here's some technical stuff to even up the balance.
The best explanation I found about the way continuations work is Sam Ruby's "Continuations for curmudgeons". Once you've read this, you'll see why Java can't do this out of the box while Ruby can.
This seems like quite an attractive idea, given the amount of descriptors needed to wire up a Struts or JSF application, and fits with the move away from descriptors exemplified by environments like Ruby on Rails. If continuations can be persisted, either to browser viewstate or the backend database, then state management can become completely transparent too, while still handling the nightmare that is The Back Button.
Intuitively it seems to me like BPM and workflow systems could gain from this approach too, based as they are on the coordination of asynchronous event-driven processes.