I know there's the not-made-here problem, but there are a number of good monitoring programs out there that are free (or free under specific conditions), including Big Brother and Nagios, MRTG and various tools that use RRDTool that would prevent you from needing to write and maintain your own.

(and for those wishing to interact with the data in perl, there are BigBrother, nagios, MTRG and RRD/RRDTool modules in CPAN)