-19
Monads simply aren't important to .NET programmers. Without even knowing monads exist you can still build the LINQ framework. More importantly, it wouldn't look any different. It doesn't matter if you think in terms of monads (Haskell), expression tree rewriting (Lisp), set-based operations (SQL), or using map/reduce to create new types (Ruby, Python), the end result is going to be the same.
In fact, I would go so far as to say that monads are downright useless to .NET developers. Every time I see a library for .NET based on monads, it is invariably both more verbose and less comprehensible than straight C# or VB code. The reason is simple, languages like C# and VB are built on much, much more powerful building blocks than languages like Haskell.
Haskell in particular needs to use monads for everything because that is all they have. The same goes for macros in Lisp or dynamic typing in JavaScript. When you have a one-trick pony, that trick has to be pretty damn good.