I almost never see ads on the net (ABP for the win), so my reply relates to television/billboard/newspaper ads:
Consciously, very often in a negative way: Some ads make me less likely to buy or even consider the advertised brand/product. These include obviously fraudulent e.g. Enzyte (not that I needed, but if I ever did, I would never consider), to the we-assume-you're-an-idiot-and-have-short-term-memory ones like Ditech, and includes the we're-trying-hard-to-exploit-your-thought-processes-but-are-incompetent-at-it ones like Sprint's.
If an ad is smart, I'm more likely to be interested in the product e.g., Sony's '80s Trinitron 5 second genius ad: A man stands by a turned off Trinitron and says "This is the new Sony Black Trinitron. But I can't show you how good it is. Not with this one" (and knocks on the screen of the TV you're watching from the inside)
I think 99.9% of the advertising I see leaves no impression at all, though.
I can't measure my unconscious response (duh), but I suspect it's nearly non existent -- I have so few brand name items that it's unlikely to have had much effect.