Micro-SIM is what all phones will use very soon. As usual, Apple is an early adopter of new technologies, and as usual, people are afraid of change, and instead spread FUD when they see something they don't understand. Micro SIM is not proprietary. It does not "lock down" the device. It's a completely standard SIM card. Just smaller.
And @minimizeme, it has nothing to do with the phones getting smaller. It has to do with the manufacturers packing more features and more components inside the phone. Making one thing (the SIM holder) smaller gives them more room to put other stuff that wasn't available (in a cell phone) just a few years ago, like GPS, touchscreens, etc.