1st for all you flamers... you're already using Linux daily and loving it since it is in ATMs, cell phones, menued answering services (well not as much in love with that one even though it beats unintelligible and/or idiotic first tier receptionist types and you can curse at bots w/o getting in trouble) automated check out counters, GPSs, many places in l'automobile, etc etc etc.
2nd someone mentioned photo or video editing and it is worth noting that there are many dedicated LiveCDs as well as installable distros. While Puppy is still a bit general with maintenance and older lappys in mind, some are much more dedicated....
64Studio - is an installable distro dedicated to pro audio recording which means it already has all the most awesome apps like Ardour (multi-track mixing/recording live and mastering studio) and Hydrogen (killer syndrums) and Audacity as well as all the great drivers and utilities like LADSPA instrument and effects plugins along with Jack the amazing plugin system with extreme low latency controllers and all that plus more tuned especially for 64bit processors.
PHLAK - Professional Hackers Linux Assault Kit - The name says it all perhaps but it is open for both white hat and black hat network uhhh assessment.
Xevia and Zenwalk - two Live CDs made especially for video editing, playback and creation like KDenlive, VLC and Cinelerra as well as a sprinkling of good audio tools and full set of codecs
Slax - with a Slackware base and Blackbox,Fluxbox, or Xfce window manager one of the fastest and most up-to-date (had Atheros and Intel Pro WiFi drivers looong before Ubuntu) Live CDs around.
Knoppix - (of course) one of the first and oldest LiveCDs comes in many flavors and is constantly being updated and tweaked. There's even one version by a forensic cop with excellent sleuthing tools as well as Stealth Knoppix, Networking Knoppix, and so on..
I've burned and used all of the above and find that they not only give one a stunning box of precision tools but create a nice rounding out of Linux know-how and all of them are great ways to introduce even the casually interested (sometimes even the ignorant and hostile) especially when one compares it to the XP analogue, BartPE, which has to get it's props being so useful and important and all if only as a great repair tool but it's frankly Little League at best compared to the worst Linux LiveCD not because Bart lacks skills but because his hands (and ours) are so tied by proprietary bull****. I am surprised though that BartPE doesn't auto-include the Linux based XP repair tool that even has the password hacker built right into it.
Have fun...cool toys and serious tools all at the same time and I didn't even mention the ones with game system (even Arcade) emulators.