HTTP-FUSE PS3-Linux has been released for using Linux on PS3 without installation. Basically the latest version of kboot downloads necessary files in Ubuntu 7.04 with CELL SDK 2.1 on demand from internet, so you need at least a flash to store kboot. What it's different from LiveCD is it's updated in remote distribution sites unlike a static CD image.
http://openlab.jp/oscircular/ps3/index.html
http://openlab.jp/oscircular/ps3/index.html