I'm pretty sure you can make great web apps with .NET, but I don't get the impression that the ecosystem is very supportive.

I found a lot more support online for other stacks.

For example, I wanted to do a tiny webpage, and host it online cheap or for free. The cheapest options were Google App Engine and AWS.

I looked into Azure pricing and ran away. I'm probably ignorant of the best solutions (Rackspace seems to have a startup program, there was a .NET hosting I liked, there's also BizSpark), but most .NET hosting was a lot more expensive than I wanted, and not supportive of "weekend project" types.

I don't know that much about Java world, however what I can say about Windows + .NET is you are less productive. Why ? 1. Linux > Windows ( For .NET ) 2. Python + Django/Flask are really powerful. Ruby & Rails as well. 3. You're basically writing and reading more code. Most of them is unnecessary. .NET is designed for enterprises. 4. Especially for startups, time & speed matters a lot. I also think some of the above reasons applies for the Java world as well. Fantastic OS projects though in Java world.