[ksm]

Likewise, we are running our SaaS product's backend with full C# -based stack (built from scratch without using any PaaS specific technologies for IPC/RPC etc.etc. so can be run on any provider) on top of Windows VMs, but database is running in Postgres. The licensing being one of the major reasons for that and avoiding SQL Server, even though it was a technology I had lot of experience from before when I was doing IT administration in MS environments. But Postgres is not that dissimilar, at least when you tend to do lots of operations in the code and not inside the DB as storprocs..

Our client/agent piece is also written fully in C# (we support only Windows workstations at the moment so it was no-brainer decision) and recently I have been looking into Xamarin to leverage that investment when moving into other client platforms.

This has worked great as I have a history purely in Microsoft technologies so the administration is lot less of a burden compared to trying to figure out everything for some other stack. If you are fluent in one technology, why not use it, right? And besides, with Mono there's at least theoretical path for running parts of the backend on Linux, but in the big picture the licensing costs for Windows vs. Linux in managed hosting is peanuts.