If you've been running a 1997-era Perl app unmodified --including the operating system of the machine it's running on, and security patches to Perl in the mean time -- you are so owned and I really hope you're not storing any important data on that box.

I'm not saying that App Engine is a panacea, but regardless of how you write your code and what technologies you use, there'll be some sort of mandatory maintenance and system administration that you have to do every so often.