Thanks to a pointer from warren, I've just pushed a workaround to the spins-kickstart repo to help some of the graphical glitches that have been seen on on the OLPC. This includes the blacked out buttons and also the cut-off text. Unfortunately, this probably won't make the Fedora 10 Preview release next week, although it will be in the final release. If you'd like to test it yourself, you can edit /etc/X11/xorg.conf and add a line
Option “MigrationHeuristic” “greedy”
below the EXA line.