I tried building Perl 5.7.3 on BeOS just for kicks tonight. It kinda-sorta worked. I got these warnings during make test:
One result of the waitpid issue is that every time you run a program, you'll get this warning: "Can't ignore signal CHLD, forcing to default".
A quick Google search indicates that Jarkko is at least aware of these issues. Hopefully they'll be fixed by the 5.8 release. I'm also hoping sockets will work (they still don't).