I have Active Corners for "All Windows" and "All Windows of Current Application". If I have a LOT of windows open, it makes sense to use the latter, which may require a quick Cmd-Tab into the appropriate app.

Either way, this still seems faster than trying to locate, in a crowded taskbar, the app that I want, and then hovering over it until it deigns to pop up the Peek interface. And if you have a lot of windows open, Alt-Tabbing through all of them, or holding a key down to wait for the cycle-through-apps-rather-than­-windows interface, is similarly slow.

One thing I will say against the Mac paradigm, is that it's annoyed me for ages that there is not a common, across-all-apps keystroke for "cycle through various windows within the current app". Not that there is on Windows, either, but of course in that case you can use Alt-Tab to go back and forth between windows within the same app. (And IIRC, within most MS apps on Windows, Ctrl-Tab gives you cross-window functionality.)