I recommended trying Symbaloo as an alternative. Since then I have heard from many readers who are happy with Symbaloo. Last week Symbaloo launched a new iPad-friendly version. The iPad-friendly version gives you access to all of your favorite Symabaloo bookmarking and sharing options in a format optimized for tablet display.
Symbaloo does offer an iPhone app, but that app is only optimized for phone display. However, the Symbaloo Android app is optimized for tablet display. In fact, I like the Android app better than the new iPad-friendly tablet display. For my taste the Android app has a cleaner, less cluttered display than the iPad display.
Applications for Education
Symbaloo allows you to bookmark your favorite websites and arrange them into tile boards that you can share or keep private. Symbaloo calls the tile boards webmixes. You can create multiple webmixes arranged according to topics of your choosing. You could create webmixes about topics to share with your students. Or you could have students create their own webmixes and share them with the class to help everyone learn from each other's research.
Symbaloo does offer an education version, but the education version is not free except for individual use which doesn't make it different than signing up for a regular Symbaloo account