Well it's a bit more specific this time, and there _are_ some, I'd say distinct, usage domains, that you could associate with certain fields:

• number crunching (engineering, insurance math; e.g. PDL as module example),
• bio informatics (see e.g. ISBN 9780596000806),
• hosting & web (e.g. embperl, mod_perl) and
• data center/sysadm things (swatch to more modern stuff like puppet, mon and rt. DBI of course).
• core computer science (e.g. parsers, PDQ)

And I think I've also seen one book about perl for some of the classic engineering sciences (sorry, couldn't find it again).