GPUs for the web
Developers have tried to overcome such barriers in the past with client-side enhancements like ActiveX, Netscape Plugins, Java Applets, but each in its own way was flawed and failed to gain mass adoption. It is possible that the Native Client project will change all this, but standardization of such initiatives across the browser landscape is a lengthy endeavor. For the near future the tools that the developer uses to provide a rich user experience remain JavaScript and ActionScript, plug-ins, such as the ones previously mentioned, are significantly limited by the architectural mismatch of performance requirements they place on the CPU.
It would be incredible, truly incredible, if hardware was designed specifically for web browsing. Can you imagine a chip designed specifically for rendering plugins? Imagine if JavaScript, Flash, and Silverlight all ran with hardware acceleration. Everything on the web would be faster, and CPU usage wouldn't be pegged at 100% when you try to watch an HD video in Flash. While I think it's cool that Mozilla is willing to entertain the idea of hardware accelerated JavaScript, I don't really see that happening. JavaScript engines are pretty fast these days. What we could really use is hardware acceleration for Flash and Silverlight (or at least a series of optimized instruction sets), and I don't really see that happening unless the runtimes are made open source.
Even if we get code running natively in the browser through the Native Client project, and HTML5 makes Flash video obsolete, I have a feeling plugins will return. It may well make sense to start engineering them with hardware acceleration in mind.