ANSWER: Amplication & Isolation. Amplication can incur issues when automated “fixes” and larger failures can make recovering more difficult (e.g. try rebooting all your iSCSI booted hosts at the same time). Isolation since a user/company can cause problems for other companies sharing the service (e.g. a DoS can effect thousands of companies). Normally, this would not be an issue with companies with separate hardware & environments. Exchange General Manager Perry Clarke explains that Microsoft is aware and has been working to improve Exchange to be the best solution for the last few years. Microsoft TechNet Blog Posting by Exchange General Manager Perry Clarke – Click HERE.