A new feature in Google’s toolbar extension allows you to send text messages to a mobile device. (I’m not really sure why this is a desired feature…) InsideGoogle has discovered that Google’s terms of service gives them the right to log the content of the text messages you send:
If you send text through SMS using Send To feature of the Google Toolbar, Google logs the number and carrier the message is sent to, and in some cases may record the text sent for debugging purposes.
What kind of “debugging” is dependent on the text of a particular message is beyond me…
MichaelZimmer.org 
Off the top of my head, I’ve had issues with the Google Toolbar before when using fancy Unicode characters as opposed to standard western characters – that’s one situation that I can think of where the characters in your message could be intimately related to a problem.
Thanks, Joshua. That does make sense. I would just feel better if Google made more explicit extactly how long they might keep records of users’ text messages.