Adsense seems to use the URLs when a page has not been spidered, I think we all agree.
So visiting www.Widget-Sales.com?CAr+Insurance will show car insurance ads.
But, there seem to be certain trigger words that trigger PSAs appearantly.
I have a website with a directory on medications. the title reads "Domain.com Drug Information" and it shows all PSAs, even though recently it was well targeted (before I made cahnges to content).
Now if I visit: Domain.com?drugs I get PSAs, but if instead I visit Domain.com?pharmaceuticals or Domain.com?Medication it s spot on taqrgeted again.
it seemss the word "drug" is some sort of black listed word and triggers PSA, even on mediapartner spidered pages.
Note that this site is not on the adsense system (I use my accoun from a different site) so that may be a reason too.
I will now remove the word "drug" from my headings (not form body copy, or it will be non-sensical) and report back if this works.
Perhaps others with PSA problems should try adding "?relatedkeyword" after the usl for the pages in question and see if the PSAs are caused by one of these trigger keywords.
Not that this is a theory and I've not tested it for other words.