I know the readership here does not represent the general population of the internet, but have any of you ever purchased a product/service from an ad served up in a non-search context?
No, but display advertising is more about brand awareness and opinion-- it's not a direct-response game measured by CTRs.
A better question is if anyone has been influenced or reminded of a brand or product as a result of an ad served in a non-search context. I know I have!