I tried it before. Brings people in, but be sure to be very specific with the key words you want or else youll get a grip of traffic that doesnt buy and your paying for them.
One thing I did do that worked well until Barnes and Noble caught on was I had ad words set up to take B & N as its key words. It would bring in my ad anytime someone typed in Barnes and Noble, BN, B & N..etc.
Made about 350/month spending about 250 of that in ad words.
I know about a month after it began BandN Emailed me telling me to stop...copy right infringments, breaking terms..blah blah blah...