Our production environment is running on Windows + IIS + .Net, but we are moving everything to Mono. It is working for us. We are working on a stack based on Debian + NGnix + Mono. We are already using PostgreSql and Mongodb as as a data storage; we use Git (@ Github) for our repositories, and TeamCity for CI.
I do agree, the OSS stack for .Net is not as nice as Microsoft's, but in my case I mostly do everything with Emacs anyways, so it doesn't bother me. MonoDevelop is not bad though.