From initial looking it does not change every user.
Here are some tidbits from what I found and need work on.
In Internet Explorer one needs the links to click to change stylesheets.
In Mozilla there is a nice little box on the bottom left corner of window that allows you to instantly change themes.
However as expected the change a user makes is only good for one window and when the page refreshes it goes back to the user's default. Basically the javascript allows switching of the stylesheets. What needs to happen is a script to be written upon action of the stylesheet change to rewrite the user's cookie with the updated stylesheet then the change would take place on how many pages the user wanted and changing would simply be clicking the box to change it. Or of course logging out. Rewriting the cookie routine on the fly is more complicated than most things but doable using the present code in threads to another script allowing the stylsheet variable when switching to be passed to the cookie.
Since I assume 6.4 has an updated cookie routine when it goes final it might be something worthwhile to look into as far as hacks are concerned.
