Sam Ruby: "While I’m not a fan of content-sniffing, one of my few pet peeves with HTML5 is that it endeavors to institutionalize the practice with no provisions for content providers to opt out. As the lesser of the available evils, I hope Microsoft’s proposal is quickly adopted by other browsers."
Comments ensue. My take? - Sam's better when he sticks to technology and away from policy-making.
Nonetheless I'll see your busted browser based content sniffing web and raise you a content gets dropped on the floor because the client sent an Accept header mobile web. I had a chat with a colleague last week who writes J2ME (and kills at it), who has had enough of HTTP purism, wants to use POST by default, wants to avoid putting anything of significance in a HTTP header. He has a point, if you care about, say, fault tolerance, or shipping.