I wonder - if it might be the security fix for the HTC loggers? (making your private information on your HTC EVO available to just about any rogue app that wants it?)
Massive Security Vulnerability In HTC Android Devices (EVO 3D, 4G, Thunderbolt, Others) Exposes Phone Numbers, GPS, SMS, Emails Addresses, Much More
I'm currently on 2.08.651.2 - and haven't seen the OTA request yet (checked manually too).
Edit: Got the update now - seems to be working ok (no noticeable changes)