After a lot of searching, I've decided to post in hope that someone can help me...
I have recently inherited a Latitude D610 at work. I've used one before and liked using the Fn + Up and Fn + Down buttons to adjust the brightness. This D610 doesn't change brightness -- even when running off the battery it's fully bright. Here's what I've done so far:
Verified that the Fn, Up and Down keys are working
Updated the BIOS to A06 (the most recent)
Installed / Re-installed the Intel Graphics Video driver
Installed / Re-installed the Dell Quickset application
Sacrificed a goat
Scoured any and all Settings and Properties screens for options