The one I find most annoying on Android is the search bar on the home screen. Even though you can customize most of the rest of the screen, you can't change the search provider for that bar, or even just remove the bar. At least, not without replacing the launcher entirely, with something like Nova Launcher (http://novalauncher.com/), which is what I eventually did.
This is not really an android flaw but a nexus one, because its default launcher is part of the google search app. On many android phones, the search box is a widget that can be swapped out with a widget from any other search provider or removed entirely.
