On more than one occasion, changing the user agent in Firefox leads to a faster Google product. It's most definitely happening, but Google hides behind the excuse that it's using "cutting edge" technology and they have compatibility layers for browsers that don't support the new features.

This would be solved if they did feature detection instead of browser sniffing, but given that the user agent hack works, they're very likely doing browser sniffing.

Better yet, they should probably wait to adopt new standards until things are actually standardized, instead of doing things as soon as they hit "experimental" status.