Some people complained how the X10 2.1 update doesn't have automatic brightness. I found a quick fix for that, and it works for me.
MUST HAVE ROOT
Just go to your Market App and search for Spare Parts, by Android Apps.
Download, and install
Open the app then scroll all the way down and you will find "Brightness mode"
Select it and select "Automatic"
Reboot your phone and test it out. I put my phone in direct sunlight then took it out, I noticed that the brightness of the screen decreased. So I am assuming that it works now.
-Theres a few other options in the app that you can play around with.