I'm sure it will help with web apps for which JIT time is a significant performance drag. But even then, my knee-jerk response was to think that faster JIT compile times shouldn't really impact the life of anyone who knows about ngen.exe.
Reading the article, it sounded to me like Microsoft's primary motivation was cutting back on their development costs by shrinking the codebase. Faster compilation was just a nice side effect that also happened to make for a sexier selling point.
NGen doesn't help too many folks with asp.net, since it just doesn't work. And for a class of x64 applications, NGen is a terrible solution because it takes so long to precompile the entire application.
I'm going to put together a more detailed article for the Codegen blog regarding motivation, history, all that fun stuff...
Reading the article, it sounded to me like Microsoft's primary motivation was cutting back on their development costs by shrinking the codebase. Faster compilation was just a nice side effect that also happened to make for a sexier selling point.