turn off Carrier IQ. For those who gave forgotten, this is the tracking software that is pre-loaded on some devices to provide the carrier with allegedly helpful analytics. Last December, Verizon said that none of its phones had the Carrier IQ softwared installed and Sprint agreed to remove it from all of their models this past January. Studies of Carrier IQ showed that it could track keystrokes, but only in the dialer app (carriers already know what phone numbers you've dialed anyway) but could also report on the URL of each website you've viewed as well as know which of a phone's applications you've used. GPS coordinates can also be captured.
Besides turning off Carrier IQ, the update also adds a "compose" icon to email and the camera has been optimized to allow for pictures to be taken in a full 5MP of resolution. Considering the paucity of changes being offered by the update, we're sure that myTouch users are happy just to have the option to disable the Carrier IQ tracking software so that they can use their phone in private.
source: T-Mobile (1), (2) via AndroidCentral