What are the security limitations of AppHarbor? I see that they support NHibernate via custom security, but could I also run NHibernate Search / Lucene.NET, or is the filesystem locked down like Heroku?
We are currently evaluating whether or not to allow writes to the file system... The thing is that while you could use it for temporary storage, we may transfer your application to another server or run it on multiple, so you can't really rely on it. So for indexing I would just recommend that you try out http://websolr.com/