We've lost a few over the years...
http://nepp.nasa.gov/whisker/failures/index.htm
I had a rough couple of days after the Galaxy IV mishap in May '98, Had to re-align about thirty+ dishes on paging transmitters scattered across half of Georgia and Florida.
That day I was fighting with getting the ST. Augustine site site back on link, after about two hours I got the call which explained why I couldn't get the bird locked back in. The redundent guidance failed and put the sat. in a "un-controlled spin" luckily they were able to get a de-orbit command to take before the thing slammed into another bird. That geo-sync. orbit is
real congested now. (no slots left)
Someone's gonna get thier azz handed to them over this one as the de-orbit has probably been out prior to the two guidance systems failing and while you still have one guidance left you de-orbit with that. They'd already moved all the traffic (except for some unneeded government system) off so they knew this bird was in pretty bad shape already.