Diagnosis: A number of App Store and Cydia applications report usage data surreptitiously to online servers. Aside from the invasion of privacy, such activities also keep the iPhone and network connections active, requiring energy and draining the battery.
Remedy: Install Saurik's PrivaCY, read this analysis, and then install a new /etc/hosts file on the iPhone.
Requirements: A jailbroken iPhone.
Tested: iPhone 3GS (US), OS 3.0.1. I have not tested each of the above remedies separately.
Results: Before, ould drain about 50% of the battery on a day with (primarily) data usage. After: Drains 5% to 10% a day.

