If reputation is that important, then StackExchange's partition strategy is actually very effective. If you want to find good coders you go to StackOverflow. If you're looking for good photographers, you go to SE's photography site. There's no need for a centralized reputation hub. The reputation of a great coder on StackOverflow can't be diminished as a result of the creation of some new SE's long tail site.

But I doubt online reputation is that important. The reason I visit StackOverflow is to find answers to programming questions, not to look for experts. As for the experts, they don't need high karma on some Q&A site to get job offers.