Hi Andy,

Microchip has a few interesting docs explaining your question.

Description: Everything a System Engineer Needs to Know About Serial EEPROM Endurance
Documentation 00537.pdf (152 K)

Description: EEPROM Endurance Tutorial
Documentation 00601.pdf (71 K)

Description: How to get 10 Million Cycles out of your Microchip Serial EEPROM
Documentation 00602.pdf (62 K)

You can find these docs at:
http://www.microchip.com/1010/supp.../index.htm

Regards,
Enrique.