The current issue of login; has an essay by Dan Geer in which he posits we have two main possible responses to mnoculture:
1. Embrace monoculture, since it allows you to get
strongly consistent risk management exactly because
everything is all alike.
2. Run from monoculture in the name of survivability.
His calculations show that we could reasonably expect that 15% of all desktops are owned. This figure reduces the level of integrity business can assume with their customers, and can imply a vast starting base from which launch attacks, for example DoS, that cascade across the system. If you have not done so, now is a perfectly good time to read up on survivability and diversification.