<p>Has anyone ever done work to get Ruby to do continuations (like Seaside on Smalltalk)?</p>

Yes, in most cases. MRI (1.8) have supported them as far as my memory reaches, Ruby 1.9 (YARV)
does it, too
, so does Rubinius. JRuby and IronRuby don't have continuations, and it's quite unlikely they will get them (JVM and CLR use stack-instrospection for security)
Ruby as a language supports continuations via
```
callcc
```
keyword. They're used, for example, to implement
```
Generator
```
class from standard library.
continuations on ruby-doc
Continuation-based web frameworks (like seaside, or one from Arc's std. library) seem less popular. I've found
wee
that claim to let you do optional continuations, but I've never used it.