Right now the used thread is 100% totally and completely useless to me. The signal to noise ratio is just skewed way too far in the "noise" direction and I can not buy well over 90% of the vehicles in there. I don't even bother looking.
If anyone knows a good site to look for a used model S I'm all ears though, I'll be starting to seriously look for one pretty soon, so far the only site I've found that seems to work is Autotrader, though the selection in Canada is mightly small (not sure how much of that is the actual limited selection, and how much is that the cars may be advertised other places instead)