For those curious, here are a set of benchmarks profiling the current flash 9 virtual machine against browsers and previous flash versions (artificial benchmarks):
http://oddhammer.com/actionscriptperformance/set4/
There are huge performance gains over previous flash versions, and some substantial improvements over current browser JS engines, but not everywhere. Mozilla/Firefox, as XUL is driven by javascript, can gain some UI performance increases hopefully.
However, it is unlikely other browser vendors will use this engine. I know that opera at least, has to tune their engine for small devices and so use different optimality criteria (memory constraints are sritical etc). Nevertheless, this means more engineers working on standards which is a good thing. Lets hope it will push microsoft to finally update IE to use proper ECMAScript+DOM...
