Proof positive my brain is turning to stone.
I'm getting there though. I can see the point of this tip.
Leopard tip roundup: Expose cheatsheet, thumbnail slider, video Quick Look - MacUserHeck, I'd forgotten about the mouse over feature in 10.4!
Exposé is super handy when it comes to getting a bird’s-eye view of all your open windows—in fact it gets my nomination as one of the most life-changing features of OS X—but it can sometimes be hard to tell at a glance which window you want. Sure, you can mouse over any window to get its title, but you don’t want to have to do that to every window to find the one you want. Turns out there’s an easier way in Leopard: hold down the option key while you’re in Exposé and it’ll overlay the titles for every window.
BTW - rule of thumb in the OS X world -- always try the option key to see what it does.