> It must be clear to the user which app each ad is associated with or implemented in.

I was infuriated to be presented with a popup ad offering me (gasp!) the chance to win a free iPad recently. This was using vanilla Opera so I was puzzled about the source. I found out that some apps will inject ads into your browser - I removed the two likely suspects. This has a "chilling effect" when I consider installing new apps since I'm weighing up its usefulness vs. the likelihood that a free app will take similar liberties.