As far as browser-based 3D technology is concerned, WebGL hasn't been on many people's radars due to the lack of available tech demos designed to showcase its power. Understandably, version 1.0 of the API only came out in March but enthusiasts are cracking on with getting some impressive work up and available for viewing. Unfortunately, until the available authoring environments provide the same level of functionality and ease of use as other tools, WebGL is unlikely to see a massive uptake in the number of early adopters.
Currently, WebGL works in Google Chrome and Mozilla Firefox. Development releases for Opera and Safari are currently under way with Internet Explorer requiring a separate plugin altogether (which isn't bad at all considering this has been the standard means of delivering real-time 3D content, via a browser, for the last 10 years).
I leave you with a small video I recorded of the tech demo displayed at the start of this post. I've used Camtasia to capture the footage so the frame rate is a bit low. Normally I use fraps but in this instance it seems that it's unable to pick up the GPU rendering for this scene (if there is any).
Check the following link to see how the demo runs on your machine: