I've updated the AUP to explicilty require disclosures:
g. When making a recommendation, whether for a product, service, or website, please disclose any affiliation. In most cases, just saying something like "my product" or "this website I write for" is sufficient.
This came up in an Applefritter Talk discussion, so I decdided I should make it explicit. I don't remember ever seeing a post here that would run afoul of this requirement, which is why it's never been addressed before. In many cases, this is also an FTC requirement.