The GPS - turn-by-turn feature for example will be missing from iOS6 for iPhone 4. What's even worse for Singapore users are that the new Apple Maps may not be functioning well. Google maps was doing great with street view, bus routes etc. With Apple Maps, satellite overlay may be bad too - with clouds blocking the buildings haha. Some feature even requires Mountain Lion on your Macbook - and Mountain Lion is again compatible with some newer Macbook models only.
This is all fine, if we can stick to iOS5 for iphone4, but we all know that apps will start to demand you have iOS6 to install and run. This will suck.
Oh yah, Youtube app will be gone too from iOS6, need to use safari to get to it.....
rant, rant, rant