From my experience of continuation-based web app, what you're dealing with is not a full continuation captured by call/cc, but rather a delimited (partial) continuation, which captures the continuation of your application logic but not the state of underlying protocols. You can implement delimited continuations on top of call/cc, and I did based on Gasbichler&Sperber paper (ICFP02), but in most cases explicit CPS wrapped in some macros are just as well worked.

It does, and so does Arc, but I don't think we've needed them in anything we've written so far. News.YC is a pretty simple application.

Can we expect to see Arc go public in the near future?