"Lack of success on the web"? Besides the obvious "Stack Overflow, Myspace, Plenty of Fish" answer, observe that many --- perhaps over 50% --- of the largest company sites on the web are .NET, as are retail banking sites, trading firms, brokerages, etc. And, obviously, something like half of all enterprise web apps are .NET.
If that all seems like it trends corporate for you, well, that's obviously going to happen when your platform costs money.
All else being equal, would I start a new project on Microsoft's stack? No. But if I was really strong on ASP.NET and completely new to Django or Rails, I'd stick with ASP.NET. It works, it works at scale, and it's far from the hardest stack to code for. I might even suggest it's better than PHP, all else being equal.
IMO it just depends on the servers you're going to be using and who you'll be working with. I would stay away, far away from traditional ASP.NET. MVC is far better, but I would only really use it over Rails if I was working on a primarily MS stack environment.
If that all seems like it trends corporate for you, well, that's obviously going to happen when your platform costs money.
All else being equal, would I start a new project on Microsoft's stack? No. But if I was really strong on ASP.NET and completely new to Django or Rails, I'd stick with ASP.NET. It works, it works at scale, and it's far from the hardest stack to code for. I might even suggest it's better than PHP, all else being equal.