If it's not in your HOA documents I don't think they can do much about it. Just get some of your neighbors to participate and make sure nothing is posted that could cause a liebel suit against you and they would have a hard time shutting you down.

Some of our neighbors did this about 2 years ago but it didn't really take off, I hope it works better for you.

Disclaimer: we don't do legal advice here.

The issues here are the ones often encountered in this forum. Some obvious pitfalls to avoid would be trademark infringement, particularly in the domain name, and posts that slander the HOA (home owners association?) or anyone else, for that matter. "Chuck's Lawn Service is incompetent - they sprayed my flower beds with RoundUp!" type posts are potentially problematic and should be prohibited/removed.

Any of these areas could be sticky if you are close to the edge, so have a lawyer and tread carefully. Remember, too, that even if you are 100% right from the standpoint of the law, that doesn't mean you can't get sued. You'll still have to defend yourself.