A bit of shameless self-promotion: I’ve just written a small extension for Google Chrome for Mac OS X that can aid Mac users to select webfonts that work well on Windows. It’s called Crisp Text and installs a button in Google Chrome that allows the user to toggle the text rendering on any web page between unhinted antialiased (the Mac default display) and hinted black-and-white (which is what Windows users will see with smoothing turned off).

It works well with webfonts, so you can navigate to any webfont-offering service that uses live webfont previews and check the screen quality in the crudest of all environments (black-and-white aliased).
It’s a one-click install at the Google Chrome extensions page (visit the link with Google Chrome, then click on Install).
After installation, you'll see a small icon:
next to the Chrome address bar. Clicking on it will turn font antialiasing off and on again. The extension is not perfect (you need to click twice on the button sometimes, and you need to activate the black-and-white rendering on every page), but it works well.
It only works on Google Chrome for Mac OS X. Windows users should use the system-wide font antialiasing switch (in Control Panel / Display).
Enjoy,
Adam
