It's easy. Just turn off all ''anti-alias'' and set ''tolerance'' to 0, use pencil instead of brush, set eraser to pencil mode. Type tool can be set to "none" - you'll get pixel font in the text, even blending options can handle pixelart (too long for this post, but this is much intuitive thing). If you want, you can use vector paths for pixel-art, draw them with pen tool, select it - later you can stroke or fill it (or make a selection). Just don't make it with quick buttons in path window, do it by selecting a function from right-clicking of needed path.

 Out of curiosity, how does Photoshop handle pixel art? I've been skeptical in using it for some time, not sure why. 

Some browsers makes bicubic interpolation, smooth one, but optimal is the nearest neighbor.

There isn't really a need to have a scaled up version because pixeljoint has a built in zoom feature. Otherwise, this is pretty cool.

Black counts as a color just like everything else, so does the white you used as background. Even if it was transparent it would count as a color.