Really mixed feelings about artists selling music to ads; I tended to agree with Bill Hicks' line about the artistic roll call. Now I'm not so fussed - it's so tough to make money in the music industry now, unless you're U2 or similar. So if advertising is what it takes to avoid taking a day job, or paying for a bit of kit, then fair enough.
And if you live in a capitalist society then you inevitably benefit from the exploitation of others. You can try and minimise it all you want, but a glance at the "made in..." labels in my clothes might reveal some uncomfortable truths. Like it or not, we're all complicit.
I have always liked Nick Cave's line on licensing to advertisers though (the answer is always no). He once said that he gets letters from people telling him how much X song means to them as it was played at their wedding* or a loved-one's funeral. He said he then couldn't bear it if those people then went on to hear that same song advertising "fucking Cornettos".
* - I still can't hear "Into My Arms" without thinking of the morning of my wedding day, sat with my Dad and best man eating bacon sarnies.