Couldn't navigate the web without it Rated 5 out of 5 stars
I couldn't imagine using Gmail or quite a few other sites without Stylish and its associated styles. It's essential, and it will remain essential as long as website developers keep putting up sites that don't quite meet the needs of their users--so... forever. There *may* be a small performance hit in using it, but the big productivity boost more than makes up for it.
And for the guy who wants a better editor, install It's All Text!, which hooks into the Stylish editor window (and any other textarea--like this one) to make sending code to your favorite external editor and back to the site/window textarea a breeze.
(By the way, this review applies ONLY to version 0.5.x and NOT to version 1.x. That being said, however, version 1.0.6 is better than previous 1.x versions, and I expect the trend will continue. At some point 1.x will be a stable, mature add-on, just as 0.5.9 is--which, by the way, works fine on Fx 3.5. It's not there quite yet, but now that I can make my 1.x sidebar and editor window look almost exactly like they do in 0.5.9, it's at least "liveable"... even with the fairly ugly and un-stylish icon.)