Matthew Hurst is pretty excited about Swivel. According to Swivel's about page, "Swivel is a Web site for curious people to explore data." They also have a cute overview of the site.
In general, I'm of a like mind with Hurst, and I'm on record advocating social visualization as an interesting research direction. However, datasets and graphs unmoored from any particular purpose or activity doesn't seem all that often useful. Besides, it's hard enough finding visual insights within a dataset much less across them, which Swivel touts as a feature.
In short, I'm not hopeful for Swivel's success, but I'd be quite happy to be proven wrong.