As a sometimes Flash developer I am conflicted about the Flash Plugin... There have been so many advances in the Actionscript language in the last few years. Papervision 3D was a huge deal but Pixel Bender is even bigger... if you don't know what I'm talking about - well Pixel Bender lets you create interactive live filters ala Photoshop's filters which means things like live distortions, live painter effects, etc.
So my point is that yes it's great to get an open standard that is working towards this same set of features, including hardware accelerated video and 3D - but it's also a major setback in terms of developing for these features. Developers will have to re-learn and re-develop all of the solutions they've created for Flash... yes some will be ports from Actionscript to Javascript but others will have to be written from the ground up.
Things like animating sound for instance. In Flash/Actionscript you can use code to 'attach' a sound to an object in 3D space and make the sound source itself pan and zoom like any other object (adjusting it's volume and stereo output to make it seem to be coming from the source's location). Use a filter on the sound and you can distort it as well so that the sound seems to 'wiggle' or 'blur' for instance.
For 3D objects, Papervision has support for things like inverse kinematics where you define a range of motion for a piece of a 3D composition so that it can only move relative to it's parent 3D object and only in certain directions... combine this with a good physics engine and you can achieve realistic interactive animations of real world objects and characters. Building support for this into OpenGL is going to be *not easy*. 3D is one thing but compositional, controllable, animated 3D is something entirely different.
Like I said, hopefully the developers working on all these great solutions for Flash will take up the gauntlet and port their work over to Javascript and discover support for the Canvas object and it's access to OpenGL, Audio and Video and then add in support for particle engines, physics engines and all the other nifty tools that Flash developers have access to (some of this is already done actually).
Like I said, I'm conflicted.