Subliminal marketing

I was talking to my co-worker who happened to notice a subliminal message in a recent KFC ad. A $1 bill was nicely camouflaged in the KFC snacker. Sure enough I checked on Youtube and I found this : http://www.youtube.com/watch?v=MunPARnI0dE

It makes me wonder whether such subliminal ads are really effective?

I looked up for some more information on companies who do such subliminal ads and KFC seems to be the one who had consistently done that.

"KFC is stepping it up a notch and actually providing an incentive for people to seek out the ad, offering a free sandwich to those who can regurgitate the hidden phrase. Imagine that: there may soon be a day when we record shows not because we enjoy them, but because advertisers have told us that they'll give us free swag if we comply." source :
http://www.engadget.com/2006/02/23/kfc-leverages-dvr-time-shifting-to-its-advantage/

Many marketers explicitly deny placing subliminal ads and television networks reject such ads when they promptly notice them. For example, ABC network had stopped airing ads that they considered had subliminal messaging.

These ads create enough stir ( especially when mixed with sex ingredient ) that its been followed by avid readers and may be the marketers have succeeded getting attention. But on the other hand, why would you want to bury a hidden message and have the networks ban your ads?

I'm curious to know what your thoughts are on this type of marketing practice.