It's been a while, so I had a quick tinker. Result: One traditional, coder-colour-cycling mandelbrot.
It's done in GLSL, so it's pretty quick (more or less realtime on my radeon 2400 here, zooming in until it hits the buffers). Control it with the mouse - point at where you want to go, then left button zooms in, right button zooms out. There's a control for visual quality (speed = blocky 2x2 pixel mode, quality = full res + 2x AA) and a control for the palette scaling (higher = stripier).
I'll apologise for the colours right now :) Other than that, there's plenty of room for optimisation. If anyone wants to try, I have some suggestions:
A segmented renderer (not sure what the correct term is). Render it at maybe 1/8th scale, then look for areas where the pixel colour varies. Render at higher res, but only render these 'interesting' areas. Continue until at 1x1... this way, you can render only the areas of the image that contain anything interesting. Very tricky to do in a shader though I think ;)
Render every x frames, but scale the image in between. This is what a lot of fractal apps do - you scale the last image smoothly so you have smooth zoom, and render a new actual frame in the background, adding it when it's done. QC isn't exactly geared towards 'background' rendering, but it IS possible (I know, because I've had different sections rendering at different speeds before now, which is a bad thing when one depends on the other ;) Unfortunately, I've no idea how to actually do that on purpose ;(
