Would you buy something from a banner?

Given that people generally ignore banners to begin with, I'm not so sure of the success possibilities, but think that there are a few potential opportunities in this space.

1) Micropayments - given the ease and comfort level users have with buying small items, particularly for mobile devices (music, ringtones, games, wallpapers, etc) I think there is potential to move this kind of instant delivery content this way. Trust seems like a big barrier to overcome here, and establishing the medium as viable with such low risk purchases seems like a good spot for a provider to get a toe hold.

2) Reputation - this is key to me, I think I might be comfortable using such a system if it came from a reputable provider that I already used. I'm thinking Apple iTunes, Amazon.com, xBoxLive and eBay/PayPal to name a few. The known quantity/quality factor would go a long way towards putting me at ease in conducting an in banner transaction.
Another side to this would involve the elements of the user experience -- if it was familiar, and standard to that in other locations where said provider conducted commerce, it would also help setup that trust level.

All in all, I think that there is an opportunity here, but also a lot of potential for one or two publicized failures (such as a "phishing" scam involving a fake banner) to end it all.