"Worse, how many of us keep tabs open as reminders of something we want to do or read later?"

Indeed I do. One of these days I'll get around to adding an extension that allows me to queue links without opening them in tabs.

Anyway, I don't understand why Tab Candy is an improvement over simple window management. Since the introduction of tabs, I've grouped tabs by purpose into separate windows, and rather assumed that's how everyone did it. Especially now that you can easily drag tabs from one browser window to another, it's effortless. No new GUI to learn, to expensive extension to install.