Furbies were lame straight out of the box, but with a little bit of electronics and programming knowledge, they can be a lot of fun.
Prime examples: when I was in college, my buddies and I had fun hacking furbies doing various things. We hacked a furby's controller and IR port to change channels on my mom's TV.
We set it to change the channels or turn off the TV, then giggle with that creepy furby laugh (HE HE HE!!!).
Another fun one: one of our fellow programming students had a GBC flash cart laying around. If you don't know what one of these is, it's basically a Game Boy cartridge with a 64 megabit flash ROM in it for uploading your own ROMs through your PC's parallel port. Anyways, we wrote some code to use the IR port on top of the GBC kind of like a universal remote, and proceeded to walk around all the toy stores in the mall with our new "toy". at first we thought it was funny to make all the furbies start singing, but then we found it even funnier just to give all the little bastards head colds. By the time we left the mall, EVERY FUCKING FURBY was SNEEZING like crazy...
Anyways, if you would like to learn how to do things similar to these with those little mechanical bastards, check out this site for documentation on the IR port, and to purchase a kit.
http://www.homestead.com/hackfurby/