I installed it and gave it a try, and while it won't replace tabs in Chimera and Mozilla, it does make it easier to manage multiple Safari windows. When launched, a small floating palette appears that lists all open Safari windows, and you can bring any window to the foreground simply by clicking on its name.
It's not a perfect workaround (the windows get reordered when you click them, unlike tabs, and it's sometimes slow to update when you open or change a window), but it's definitely a nicer way to manage multiple open pages than the alternatives (cycling through all, mousing to the dock, or mousing to the menus).
I'll personally stick with Chimera/Mozilla until Apple finds a better way to handle multiple pages in Safari (though I use Safari for loading large sites and I keep it open with a few of my "information" sites (CNN, etc.) always loaded). And now, I'll leave the Tabbed Safari script running to make it easier to pop open the exact informational page I want to see...

