[janpieterz]

You can indeed run a forum community but offload the work to Amazon. Speaking about that, you can easily run everything on Amazon, because the latency between your webserver and the database might become a problem.

Privacy concerns wise, Amazon and Azure and the sorts are probably way better protected than your own installation. Of course the privacy with Amazon and Azure are all clearly written in their terms of usage and privacy statements. And NSA wise, if they get into an Amazon (either politically or technically) they will easily be able to hack your own installation.