I think Undisclosed posting is an important feature. Many individuals that I know in client companies are prohibited from "endorsing" a product in public forums, and simply describing a good experience--although truthful--constitutes an endorsement from their employer's perspective. Yet there is a great value in hearing the specifics of someone's discoveries and experiences in technology deployments, whether or not the name is disclosed.
There are many situations in which Undisclosed posting is appropriate or required.
I think your policy on handling Undisclosed posting is appropriate.