I actually find Google's higher weighting of StackOverflow results annoying. I've recently been experimenting with a new iOS project, and whenever I search for something Objective-C or iOS SDK related, the first few results are SO questions. In some cases this is useful, but for many queries you really just want the canonical explanation from Apple's docs, not a bunch of people discussing an issue that happens to include those keywords.
SO is more useful when you have a problem that you're trying to debug, and official docs are more useful when you're trying to understand new concepts. Unfortunately Google doesn't allow any way to differentiate between these modes.