After installed Ubuntu 10.10 Maverick, Alt+PrintScreen key combination to take a screenshot of current window stop working. Actually, it is because Alt+PrtScn is in conflict with Magic SysRq key.

You can get Alt+PrtScn work in Ubuntu 10.10 by disable Magic SysRq key with this command in terminal:

sudo sysctl -w kernel.sysrq=0

If the setting disappears after reboot, just add following into the file : /etc/sysctl.conf

kernel.sysrq = 0

To enable Magic SysRq key, use:

echo 1 > /proc/sys/kernel/sysrq

or

sysctl -w kernel.sysrq=1

More about the bug, read: https://bugs.launchpad.net/ubuntu/+source/metacity/+bug/642792