I did a little reading on the web and didn't find an easy way to turn off the updates. After seeing a few helpful notes on various forums, (this tweak in particular stands out) I saw some favorable feedback on 9.0, although there are still complaints about bloat. Adobe added the ability to update preferences in Reader 9.0, which didn't exist in Reader 7, so I decided to give 9 a try. To disable updates, click edit, preferences, general, then remove the check mark from "Check for Updates" under Application start up. With automatic updates disabled, you can still Check for Updates manually by clicking on the Help menu. Here is a composite screenshot showing the setting to disable updates for anyone who needs a clear picture.
PS. After the original post, I learned the same preference is also in Adobe Reader 8.
Happy New Year,