Is there a Safari 5 extension along the lines of Stylish? Basically a way to quickly install or create site-specific CSS files.
Extension in development, but you can create new styles, search/manage/edit styles from user styles.org database, styles options - only default values supported in current version.
It appears as though an independent developer has ported or rewritten Stylish as a Safari extension! It is currently in beta according to the developer.