What the Hell can .Net do exactly?

What's an example of a possible application that can be made with .Net?

What's a current example of an application using .Net?

JIT would be compiling bytecode to binary executable. It doesn't take long because bytecode is already quite close to binary.

gcc can actually compile Java sauce/bytecode to binary if you ask it nicely.

Flyweight programming can vastly reduce the overhead of objects. This is why Swing is so fast.

Something I would like very much would be access to the garbage collector so I could turn it on and off during speed critical sections of the code. Most other garbage collected languages give you this ability.

It's worth noting that raw execution speed is becoming less important than expressive power - that is to say as processing speed tends towards infinity, the time it takes to write, debug and maintain the program is becoming more important. It's now far more desirable to have a program that is 10 times shorter than one that is 10 times faster.