Haven't seen the ads. This may be completely unrelated, but I found this press release from Gap inc.
http://www.gapinc.com/public/Media/Press_R...lJuly2805.shtml
It mentions the release of a CD from gap with 8 exclusive recordings of "Classic Songs for New TV Spots"
And here they are, possibly one of these is what you heard, although I have no idea really.
Alanis Morissette “Crazy” (Seal)
Joss Stone “God Only Knows” (Beach Boys)
John Legend “Hello It’s Me” (Isley Brothers)
Michelle Williams “Let’s Stay Together” (Al Green)
Jason Mraz “One Love” (Bob Marley)
Keith Urban “Most People I Know Think I’m Crazy” (Billy Thorpe)
Brandon Boyd “Alison” (Elvis Costello)
Liz Phair* "Cheek to Cheek" (Irving Berlin)
And in fine print, liz phair's song is not included on the cd, instead the song
"Life on Mars" performed by Michelle Branch
is.
Good luck.