Well, they do not send out very much interference, but its something to keep in mind. I once talked to an engineer at Gateway, and he told me that major OEMs needed to have their computer cases FCC approved, so that they do not send out any waves that could scramble things.
A good example, would be a long time ago when windows became popular. Some guy did a window mod, and all the sudden his garage door remote stopped working. Then the neighbor next to him suddenly had a garage door that would open and close when ever the computer was turned on. He put foil over the window, and eveything went back to normal.
This was a famous story about 2 years ago, so I'm sure someone else remebers it.