What I would like to see...
are some benchmarks comparing this to Silverlight & Flex. From my own personal testing Silverlight seems to run about 20X fast than flex due to JIT vs interpretation. Javascript is really an apples to oranges language since methods, classes, properties, and anything else can be changed dynamically at run time. But most of the time that doesn't happen, so I would think that JIT compilation should place JS at around 90% performance compared to native code.
Oh wait, here they are... thanks Google
http://lambda-the-ultimate.org/node/3851
http://channel9.msdn.com/shows/Going+Deep/E2E-Tracing-JIT-and-SPUR/