buckworks - 6:19 am on Jun 1, 2010 (gmt 0)
Captaffy, I strongly agree that too much exposure can become a negative thing. If it starts to feel like "stalk the user" that advertiser has poor skills.
For the account I mentioned, we set the frequency cap so that users won't see more than five banners per day from any one ad group.
If someone is doing enough research in the sector that they encounter us more than that, they'll at least get a different banner for a different product.
The frequency is a judgement call on my part, and we're still experimenting, but common sense says that overdoing the exposure can backfire so keep a light hand about it.