I have an IBM T23 with the same problem. I don't know about Feisty (I never used it because of other problems), but it was working in Gutsy a few days ago. There were some updates, and now it doesn't seem to be working. The indicator pops up, but the indicator just stays all the way at the bottom, no matter where the brightness is. At maximum brightness, continuing to press the up brightness keys will make the indicator move one notch up, but then back down again on the next press.
I have an IBM T23 with the same problem. I don't know about Feisty (I never used it because of other problems), but it was working in Gutsy a few days ago. There were some updates, and now it doesn't seem to be working. The indicator pops up, but the indicator just stays all the way at the bottom, no matter where the brightness is. At maximum brightness, continuing to press the up brightness keys will make the indicator move one notch up, but then back down again on the next press.