Watch out for possible liability for defamatory content - the Communications Decency Act [1] may provide you with some immunity from liability, but there are cases suggesting otherwise in fact situations not dissimilar to yours. [2][3]

[1] http://en.wikipedia.org/wiki/Communications_Decency_Act

[2] http://www.citmedialaw.org/sites/citmedialaw.org/files/2004-...

[3] http://www.citmedialaw.org/sites/citmedialaw.org/files/2005-...