I actually tried to build Perl 5.8.1 on BeOS a couple weeks ago. I think I heard my computer laugh at me.
There's no real point in trying to work out the bugs, though, with Zeta coming out soon. Perl will supposedly be included in the Developer's Edition, so I dunno if that means they're working on getting 5.8.x working well or if they're just going to ship a broken Perl.