so, how do you design a system that gives people the news they actually want to see?

hey ppl im thinkin bout buildin a news aggregator w personalized feeds, yknow? the plan is to show articles based on what ppl read, topics they like, and maybe even when they're reading. im wonderin whats the best way to scale this. should i go w collaborative filtering, content-based, or a mix? how do you deal w new users or articles when you start out? any ideas on data structures and databases that would work for this kinda recommendation engine