I wonder what limitations or cutbacks the free Bing edition would have.
For example, Bing related Start screen / quick-launch / desktop icons that cannot be deleted. Another thought would be any time you do a Google search in Internet Explorer, a pop-up appears like “Not satisified with your search results? Try your search again in Bing!”, etc.
Another posssibility would be like the Windows 7 Starter edition that came with Netbooks, e.g. where personalisation was heavily crippled, requiring third party software to change the desktop wallpaper, colours, etc.