I'm running Ubuntu 10.10 on a Cr48. I'm attempting to bind xbacklight -dec 10 to f6 (decrease brightness in chrome os) and xbacklight -inc 10 to f7 (increase brightness in chrome os). The decrease command works fine, but the increase command appears to have no effect. It's the same whether I run the command from the command line or use the bindings I set in CompizConfig Settings Manager.
You can change the brightness by changing some setting files.
I hope this helped you and I don't know if it's possible to fix this bug with xbacklight. If you really want to work with xbacklight, I'd create a bug report.
I had this same issue at first... I think it's that the default is to take 20 steps to complete the transition... this combined with your small 10% change breaks things it seems.
I got mine to work by making my functions as such:
brightness up => xbacklight -steps 1 -inc 20 brightness down => xbacklight -steps 1 -dec 20
But if you setup your steps to be 1 and increase your percent changes to 20 or more you should be just fine with xbacklight!