I used it on iPad a little so I was excited to see it came out for iPhone. Have used it a little bit, but I think I slightly prefer Zite on both devices. It isn't as sexy, but I think the layout is just a bit more efficient.
Plus, the point of these things is suppose to be to get NEWS. If it looks cool, great. But apps like these are basically glorified RSS readers that do the setup for you. For that reason, if I really want all the news I missed from the last 12-24 hours, my first stop is going to be an RSS reader (I use the free version of Feedler, which hooks into Google Reader account).
But both Flipboard and Zite are free apps, so if there's a news source that's free and works, I definitely keep it on my phone! The Facebook/Twitter integration is kind of neat.