I’ve done a little bit of testing with Raphael and, anecdotally, I’d say that it’s slower than the native SVG rendering, which you’d expect. This isn’t to say that you shouldn’t consider Raphael for mobile devices, it really does depend on the kind of application you’re building.
For charts and graphs, which tend to be graphically simpler than something like the map in my example, I really do recommend using something like Flot.
There really is a place for all of these different approaches, and even a mix. It’s an amazing time to be a web developer.