Of course, my family is European. They 'get' texting. They then didn't ask "So what is that for?" like they do for Hyves or Facebook and then discuss whether to let their children on. No, they understand an SMS stream, the irreverence that follows, what exactly the potential for conversation is.
Oddly enough, I think I also need a metaphor when explaining Twitter to a certain category of technology worker, one that is totally into computers but still can have Luddite tendencies. People who crunch Fortran in their sleep but get disgusted by phones that might do something else than just take calls (although they are amenable to feature creep as I have written before...). They post to Slashdot a lot, but they don't understand what Twitter could ever have as a value. I think I'll try explaining it as "Asynchronous IRC". Maybe that will instantly convey its strange conversational ways.