I use it to read Hacker News -- I leave it on the 'all' filter and scan the new items a couple times a day. The browser extension lets me see which comment threads I've read that have new comments, and then highlights those new comments for me. At the end of the day, I'll usually filter it down to the top 20 to see anything I might have missed.
I use it as metanews as often as news - if there's a big piece of news, I don't have anywhere else to pick someone's brain about it than HN.
Sometimes I just browse the general index serendipitously - often with great success.