Tom Beddard has released Fractal Lab ("A WebGL based web application for rendering 2D and 3D fractals in real-time".)

The current limitations are that it runs in google Chrome or Firefox 4 Beta, also the compile time takes a little while on Windows
as the shaders must be converted to DX from OpenGL. If you run a Mac this isn't an issue. Once the compile is done for each
fractal type you can tweak other settings in preview mode and navigate to "places" in real-time, ...amazing!

The link is here:

http://www.subblue.com/blog/2011/3/5/fractal_lab

The more power your GPU has, the the better/faster a final image can be rendered.

Here's a "place" I went, sized down from full screen (1920 x1200):



I'm looking forward to future updates (maybe panorama/animation capture), but Tom has done a great job so far!