I highly recommend Log::Log4perl for debugging -- you can set the messages to DEBUG during development, then wind it back to WARN for Production.

If you start to see a problem, you can turn the logging level back to DEBUG -- without touching the code -- to identify the problem. This is a lot nicer than print statements in the CGI, because you can diagnose the problem in Production code without the customer knowing ("Hey, how come I have all these comments in my web page?").