For those interested, the 'Screen dims after ..." still works in 3.x.
(Remember the old Extended Preferences, Supreme Preferences, etc option ?)
This along with Notifier, and custom backgrounds are my minimum iPhone requirements 
Sure most of you knew this (haha), but here is how to add natively.
Note: Sorry, I'm not going to provide more detailed instructions. Why? Because if you mess around with this file without knowing what you are doing it will screw up your phone.
Add the following lines to /Applications/Preferences/General.plist immediately after the 'setScreenLock:' dict item:
HTML Code:
<dict>
<key>cell</key>
<string>PSLinkListCell</string>
<key>default</key>
<integer>60</integer>
<key>defaults</key>
<string>com.apple.springboard</string>
<key>detail</key>
<string>PSListItemsController</string>
<key>key</key>
<string>SBAutoDimTime</string>
<key>label</key>
<string>Screen dims after</string>
<key>validTitles</key>
<array>
<string>15_SEC</string>
<string>30_SEC</string>
<string>1_MINUTES</string>
<string>NEVER</string>
</array>
<key>validValues</key>
<array>
<integer>15</integer>
<integer>30</integer>
<integer>60</integer>
<integer>-1</integer>
</array>
</dict>
Usage: 'Auto-Lock' must be set prior to 'Screen dims after".