Yahoo answers and CPA - Good or bad idea?

It converts and converts well but it's a technique that you need to do properly, it's not something you can spamfest or pay some guy $2 and hour to do for you.

I have a collegaue that uses it quite extensively but only in very high ticket items, predominantly private programs paying $150 - $200 a pop commision in the financial sector.

You need to actually offer quality advice, you need to actually (God forbid) know your subject.

If it's done right it's powerful because:

a) YA, has great positions in SERPS and lasts almost forever.
b) People often link to a good YA question/answer
c) The gen public generally trust YA responses if the feedback on the guy is good.
d) You can of course manipulate your popularity and rating quite easily.

Bottom line yes it works but I think it's an awful way to promote stuff for $20 commision unless you hit a jackpot, but for a more long term, high value product that's worth putting in the time to actually help people and become a mini authority , yeah it's solid.