I think emulation is a great tool for quickly producing software that can be run on a real Amiga - especially for people like me who only have a basic Amiga.
As far as emulating software that requires exact timing / hardware tricks such as games or demos I still haven't seen anything that runs without glitches (as brilliant as emulators such as WinUAE are).
I think a lot of people don't like emulation is because of inaccuracies that may give the wrong impression of the machine it is trying to emulate. I'm yet to see an Amiga program scrolling 100% smoothly on a PC under emulation - sometimes details like that really do injustice to games and give a bad impression of what a real Amiga is like.
In sort: Emulation is great, but for accuracy you need a real Amiga.