http://aka.ms/wpdemo on one's iOS or Android browser, you'll be immediately tunneled into a emulation of Windows Phone 7. We gave it a test run here at Engadget HQ, and it seems that every tile and swipe save for Apps runs properly. Can't say the fonts and such looked as smooth on our Galaxy S II as they do on the Radar, but it's a solid effort that'll definitely serve you well if you're considering the switch. Just don't try to flip the demo horizontally -- that's clearly a no-no.
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Windows Phone 7 emulator within Android 2.3's web browser