Here's a snippet that really clicks with me:
O: I still can't hear "Good Vibrations" without thinking of Sunkist.
TW: Oh, wow, yeah. That's exactly what they want. They want to plug your head into that and change the circuitry. While you're dreaming about your connection with that song, why don't you think about soda or candy or something? It's too bad, but it's the way of the world. They love to get their meat-hooks in you.
Mr. Waits has a great point. Combine a song (popular or not) with a commercial and chances are good you're going to remember the product and the song. Yes, I know "advertising works" but when a song not originally intended to used for an advertisement is used in one, which is more memorable in the long-run?
I say the song is the one that stands out longer only if it's not attached to the commercial forever. State Farm will probably always be remembered for their "And like a good neighbor/State Farm is there" jingle but that's their own jingle. In the case of Circuit City currently using the Cars' "Just What I Needed," I think of the flashy commercials with laptops and flat-screen TVs more than the band's album covers or video for the song. No matter how much I like the song, I'm still not going into Circuit City (when you have Best Buy and Frys in town, why bother?).
Then there are songs that were once used in commercials that aren't anymore. Given the amount of time and the people not exposed to the commercial, chances are good that there won't be a connection to a commercial. Case in point: I believe Carly Simon's "Anticipation" was used in a Heinz 57 ketchup ad in the '80s. Since I vaguely remember the commercial (a pre-Friends Matt LeBlanc tilted a bottle on the roof of a building and bought a hotdog just as the ketchup flew down), I vaguely remember the usage of the song. These days, I remember the song more for its opening line ("We can never know about the days to come/but we think about them anyway") more than anything else.
In the case of Nick Drake's "Pink Moon" being used in a VW commercial, I don't think of VWs when I drive around to his music. Reminded of the moon shot in the commercial, I tend to look up to the night sky when I have the song on in my Toyota. I'm not thinking about how I should own a VW, but it keeps their name in my mind.
Advertising is a really sneaky medium. Ads get into your brain whether you like the product or not. While I'm not one to become a zombie and think that because of Circuit City using a Cars song I must buy my next TV from them, this kinda spoils the enjoyment/privacy of listening to music. Sure, using songs in commercials may be a good thing for an unknown artist getting its name out, but most artists don't set out to be jinglemakers.