in reply to Creating threads inside BEGIN blocks
I think it depends very much on which version of Perl you are using, and lately, which version of threads.pm you are using (as threads now is dual-life, so more up to date on CPAN than any non-blead/maint perl).
My personal experience on Linux was that some warnings would occur on process exit. I haven't seen those for a while now. But then again, I haven't been doing much with threads the past 2.5 years anyway.
I hope someone with more up-to-date information will be more able to enlighten you.