I suppose this has grown popular enough to warrant it's own FAQ.
Speed painting has been defined in the past as follows: (although
they slightly vary from week to week)
1. You have approximately 30 minutes (try to limit differences by 10
mins, give or take) to do a sketch/painting/model, digital or
traditional of the supplied topic.
2. Time dedicated to scanning, uploading, saving, etc, is NOT counted
towards the time it takes you to do your entry. Just the time you
spent creating it.
3. You can submit as many entries as you want.
4. Much like the monthly sig competitions, the previous winner
decides the next topic and the next winner of said topic.
5. Have fun! Obviously there's no way to tell how long you *actually*
spent making the image, so this thing runs on an honor system.
If you're interested in what topics have taken place in the past...
Search the photoshop archives for "speed painting" and all of the
topics will come right up for you.