Google native client is a promising tech for web to reach desktop performance. I developed a complex vector application (htp://www.torapp.info) and reached better performance than desktop equivalents.
I find it hard to believe, because even that it runs native code, there is a small penalty of a sandbox environment and it certainly cannot be faster than pure native code.
Just because desktop always wins in theory doesn't mean that you can't exceed the performance of existing native clients. I'm sure Illustrator leaves a ton of performance on the table simply by virtue of having a large legacy codebase. For instance, if it becomes practical to assume that all of your clients support GPGPU then Illustrator's existing CPU optimized code instantly goes from being a critical advantage to a heavy burden: they have to maintain that code and write new GPU code that somehow fits with the old code whereas you just have to write the GPGPU code. Witness pixelmator curb-stomping Photoshop in the performance department. Of course, that example is Desktop App vs Desktop App but the principle is the same.
