I don't remember an annoying header bar, and that's beside the topic of algorithms and content. I do think the UX of circles themselves were much better than e.g. Facebook lists-- circles were much more visual, easier to add/remove people in (drag and drop!), and much more central to the posting experience, which all made them easier to understand and more universally used. Facebook lists feel like an after-thought that only power users even know about at all, and Twitter hashtag/word block lists feel like a heavy-handed last resort rather than something everyone's supposed to use.