Yellow Dog Linux 6.1 is quite capable on the PS3 for running OpenOffice.org, Firefox, watching high definition videos, etc, etc like you can on a PC. But I found this interesting, Win95 (which is x86! and thus very hefty to emulate on the Cell's PPE, which is PPC) and then running Starcraft:
http://www.youtube.com/watch?v=zQHlFPRPhHA
Maybe useful to a few if you are using a keyboard and mouse on your PS3 and want to play a RTS. To me its more interesting this runs at all and actually works pretty well! Looks like SPE usage in Linux is increased.
Early 68k MacOS and AmigaOS releases are also already emulated on the PS3 using Yellow Dog Linux and usable enough to run some classic applications.
Regarding games emulation Snes, Amiga and classic Arcade games are fun to play, if for example you want to use the wireless PS3 controller and want to play on your living room HDTV.
Arcade games running on the PS3:
http://www.youtube.com/watch?v=9T2g2ekZETs (YDL 6.0)
Amiga games:
http://www.youtube.com/watch?v=bEklKwJoyjI
