use Perl

"The language is still changing, there is no spec for the language, there are going to be differences between implementations that are essentially undefined behavior."

The Register has an article about Ruby.NET with a lot of quotes from the project manager, John Lam, such as the one above. However, the spec is not something they can do anything about, so they have no choice. But one that caught my eye was one they do have some choice over:

Some familiar features will not be implemented, however. "Call with current continuation, we're not implementing that. [Although] JRuby isn't either. ...

It makes me ask myself a couple of questions, but not being familiar with Ruby or .NET, I don't know the answer to either. Does my usually silent readership know:

• How often is call with current continuation used in typical Ruby programs? Would its absence be noted frequently?
• Why do both the .NET and Java VM implementations of Ruby choose to omit it? Are continuations something stonkingly hard to make work well on their VMs? Would such a problem constrain any attempts to make Perl 6 run nicely on the VMs?