Whenever you see a spark when making an electrical connection, it means there is current flowing, even when "off".
Back in high school, I once watched some friends try to and start a car with a short. When the battery cable was connected, there was a huge spark.
One friend had the bright idea to just leave it clamped on, and just fix the burned up wire later.
Needless to say, in a couple of minutes the dash was in flames and we were running for a fire extinquisher.
Some devices draw a heck of a lot of power just being plugged in. There was a recent artical showing the Playstation3 drew something like 20 or 30 or 40 times the amount of power as a Wii.
Just to be on the safe side, I'd recommend going through the house electrical system and making sure your dishwasher/microwave/etc.. are all on seperate breakers. You can by an inexpensive inductive ampmeter and hook it around the wire in the basement to see how many amps are flowing under load and if the wire is rated for that.
Don't run computers on the same leg as bathroom hair dryers, kitchen blenders, etc...
Also, make sure the 14gauge wires going into the fusebox aren't on a 20amp breaker-things of that nature. I'm no electrician, but sure learned a bit with a new house purchase.
In the meantime I'd be calling the store and checking for recalls.....