Annoyed and somewhat confused by some the crazy stuff I'm needing to do in order to get the Strawberry additional libraries to install, I've decided to finally end my intentional ignorance of all things C and picked up the cow book from my local book shop (it had the most content of building code, pre-processor stuff, and C modules, which is where my biggest needs are).
I consider this a failure, as I have long-valued NOT having to know C in order to work with Perl. And on dozens of occasions it has helped to be able to play the "I have no idea what you are talking about, explain it in Perl terms" card with people that seem to assume all Perl programmers (or at least all CPAN authors) know C.
Given the number of people that have problems with unreliable C modules, I also consider it a positive thing that all my modules are pure Perl. The temptation to do things in a faster but more evil or harder-to-maintain fashion has also been one I haven't had to deal with.
The only positive is probably with regards to career options, as some of the better-paying toolchain/build-system jobs (including one recent $US200k one in New York) require C knowledge.