Writing regex in PL's

Is there anyone on this list who has preferred to use regexes from PL's
(e.g. plperl, plruby) in CHECK constraints or other places instead of
the flavor provided by Postgres? Do you find your approach satisfying?
Do you also do things like cache the pattern so you don't have to
compile the regex on every function invocation?

I'm also about to choose this route, mainly because I want to separate
the patterns into a Ruby module and would rather have one regex flavor
(and I can never remember all that POSIX stuffs anyway :-).

--
dave