programming multithreaded applications in perl

Hi,

in the perlfaq1-manual, there is the following statement:

"For various reasons, Perl is probably not well-suited for real-time
 embedded systems, low-level operating systems development work like
 device drivers or context-switching code, complex multi-threaded
 shared-memory applications, or extremely large applications."

Unfortunately, the reasons are not explained. I am a PhD-student at a research 
group, where parallel processing is a big issue, and I was wondering if it 
was possible and feasible to program parallel applications in so called 
scripting languages, perhaps trading development time for performance in the 
process. Well, it seems to be possible, as ithreads seem to be working. So I 
was wondering, what these unexplained reasons are? Is there a document or a 
posting somewhere, that state these explicitly? Or is this just plain old 
information?

Thanks for your help,
Michael Suess