The Doom on the Web demo has been viewed over 35,000 times so far. Based on the responses, I'd like to clarify some things that I should have mentioned before (sorry for not doing so).
First off, I should have linked to the details page more clearly. It explains a bit about the demo, where it is currently known to work, etc.
Now, to the main issue: This demo is not a good benchmark of anything. The goal here was not to run a version of Doom with good performance, but to run DOOM itself, the original, with as few changes as possible, on the web. I made no effort to optimize the code, which was written and heavily optimized for a completely different architecture (it uses fixed-point arithmetic! :) I wasn't sure if it would be playable at all.
That is, the point of the demo is, "Doom can be run, with hardly any modifications, on the web." Showing that sounded like a cool thing to do, so I spent several evenings and a weekend or two on it.
As for frame rates, Doom caps them at 35 - you won't see it get any better than that, simply because of how the main loop works (and as mentioned before, I didn't try to improve it). It will also max out your CPU, even if it doesn't need to, for the same reasons. It might be possible to optimize this with some modifications to the Doom source code, but I didn't look into that. So, if you are seeing 35fps and 100% CPU, that doesn't mean your machine is actually working hard to generate it.
P.S. I apologize for the quality of sound in the demo. I never used any audio generating API before, and I still don't know what the numbers I am passing from Doom to the Audio Data API actually mean ;) I basically just hacked together something quickly, got it to the point it is in the demo, and stopped there. Someone that knows this stuff could probably make it sound right.