It's really all in the User-Agent string, and maybe a few other headers. All browsers have certain quirks that you could look for - but that wouldn't necessarily give away anything secret. The User-Agent string can very easily be cloaked however. Konqueror, for instance, let's you customize it by domain.<p>Furthermore, I doubt Apple would test it's product on the wide-open web very much. I'm sure it has it's own internal network to test things on, and it's own set of browser rendering tests.