In my experience, from a short-term business point of view (read: how most people think), you're looking for the balance that stops just short of being such bad UI that people actually decide not to use it; but getting almost that bad is just fine, if it drives up banner impressions.
Personally I prefer to stay clear of anything that's actually annoying to users; I mean annoying as in genuinely annoying, rather than just "people will complain". For example, road block adverts (like when an entire page is taken over with an advert saying "your content will load in x seconds") are genuinely annoying, a sponsored site skin is (unless it's implemented/designed badly) not, because while people might see it and mutter to themselves, it doesn't actually harm their use of the site at all, and it's not nearly annoying enough to make them leave the site.
Interestingly, on one of my company's websites (our entire business is based around advertising), we had discussed the possibility of doing things like this and decided against it, on the logic that even though we wouldn't directly drive away users, in the long run it might contribute to their not liking the site as much. However after various pieces of user feedback, we ended up doing just this for galleries that our journalists take at events, now each image loads a new page cleanly, (giving new banner impressions), and feedback since we made that change has matched the suggestions we had beforehand: our readers actually prefer it.
Personally I prefer to stay clear of anything that's actually annoying to users; I mean annoying as in genuinely annoying, rather than just "people will complain". For example, road block adverts (like when an entire page is taken over with an advert saying "your content will load in x seconds") are genuinely annoying, a sponsored site skin is (unless it's implemented/designed badly) not, because while people might see it and mutter to themselves, it doesn't actually harm their use of the site at all, and it's not nearly annoying enough to make them leave the site.
Interestingly, on one of my company's websites (our entire business is based around advertising), we had discussed the possibility of doing things like this and decided against it, on the logic that even though we wouldn't directly drive away users, in the long run it might contribute to their not liking the site as much. However after various pieces of user feedback, we ended up doing just this for galleries that our journalists take at events, now each image loads a new page cleanly, (giving new banner impressions), and feedback since we made that change has matched the suggestions we had beforehand: our readers actually prefer it.