Just out of curiosity:
I put a link to a free-for-non-commerical-use web application I am affiliated with in the community ads section.
Now a moderator locked and deleted it telling me rules I did not read anywhere:
Ads for services you are affiliated with - especially for commercial services - are absolutely prohibited.
The application is similar to Dropbox which seems to be tolerated in the community ads section.
Is there kind of hidden (at least to me) policy page that states the rules and explains also why Dropbox seems to be OK?