I've make a habit of trolling the "There is something wrong with your computer" scams (I get a call ever 3-6 months and string them along for fun/public service)
I'd say about 50% actually know there running a scam, these will put the phone down the moment I start stringing them along (Me:Just a mo while I turn on my computer. Them: [click]). The other %50 act bewildered and answer back when I do the reveal and tell them I know its a scam, if they were in on it they would just ring off and get to the next call.
Its quite interesting to watch how their script develops. Originally they would talk me through opening event viewer so they can show me all the thousands of your computer is going to die warnings.... now they go straight for the logmein and the like. I used to have great fun pertending to boot a Windows 3.1 box and fire up Mosaic (with lots of crashes stringing it out). I'm going to have to perpare a virual machine so the can log in... I'm not sure what theme to go with