As i really like Steam i created a new special release with some nice features for steam users:
a) in gfxdetect mode you can play games with accellerated drivers
b) you can do a normal hd install - maybe onto an ext4 partition of an external drive (select the mbr of target device and do NOT boot via efi if you want it really portable) - gfxdetect works for hd installs as well!
c) it is possible to use that hybrid mbr/uefi iso with persistent mode too (just reboot to activate)
d) in case you use c) you can also mount a Win ntfs partition via dolphin and Steam lets you select this partition as install target, you don't need to install everything on a slow usb key
Btw. it is Debian Wheezy based + libc6 2.17 from Debian Experimental.
PS: I selected the drivers to match the Steam recommended ones. Basically i could create images with Nvidia 304.xx or Fglrx Legacy as well - but not this week ;)
If you visit CeBIT and want to meet me let me know.