I found this page while searching for the exact same thing as you, Jim. After a little bit of searching and trial and error, I found two solutions that I will share with you.
FYI, Jreed, the reason this feature is nice is because I don't want my Droid X to auto-rotate 99% of the time - it's just annoying when it does. The only time I really ever want it rotated is when I'm looking at pictures in my gallery or for the occasional web page that doesn't display well in portrait mode.
So, option 1 is easy, however not exactly what you asked for - Go to the market and download "Auto-Rotate Status Bar Switch" by friedflow. It puts an option in your pull down notification bar that you can pull down, click and it will toggle your rotation setting without ever leaving your app!
Option 2 requires two apps to complete, but will do exactly what you want. First download "SmartBar" by APS Technology and "AutoRotate Switch" by Kenneth Cheng. Install both apps then open SmartBar and go into "Smart Bar Settings" at the very bottom. Scroll down until you see "Long Click Camera Button" - click the checkbox and select AutoRotate Switch from the drop down menu, save and bingo - you've got it! It works so quick on my DX too, no lag at all.
Hope this helps!