[Trezoid]

Stylish[1] exists on both chrome and firefox, on all OS's with no other requirements and a gallery of nearly 50,000 styles with support for variables.

I don't really see how something limited to a single OS/Browser combo is particularly useful by comparison.

[1]http://userstyles.org/

[christiangenco]

I think the advantage lies in being able to use your own editor as opposed to the clunky in-browser editor in stylish or tedious copy/pasting between each iteration. I'd much rather work with this when developing new styles.

[wamatt]

Agreed, or userscripts.