The drivers in the kernel (0.0.5) are too old to use DDR mats properly (the functionality was added in 0.0.6, go figure) and are far too old to use Xbox 360 controllers (I plan to buy one soon). Is it possible to grab the new version from the CVS repo and add it as a patch to our kernel? I tried it myself and it almost worked, but it never made a /dev/input/js0 device and event3 (which is what it was mapped to) is, according to KDE and qjoystick, "not a joystick device."
Please mail the driver authors about this and encourage them to update and fix it in the upstream kernel. That way it will automatically appear in Gentoo and other distros too.