Mountain Lion, Apple's new Mac OS, has overwhelmingly positive reviews, from both critics and users on the App Store. With over 3,767 ratings, 3,156 of them award five stars to the OS, and it has an average rating of 4.5 stars. A small contingent of users vocally dislike it, though: There are currently 190 1-star reviews. And the overwhelming majority of them focus on a single complaint: AirPlay mirroring, which seamlessly beams whatever's on your computer to an Apple TV and is one of Mountain Lion's most touted features, isn't supported by their relatively recent Mac.
A sample one-star review:
Apple I am truly disappointed with Airplay only working on "newer" iMacs and MacBook Pro. Spent my money for just this feature. For the first time you guys and gals have truly disappointed and not executed.
Apple officially lists the following machines as AirPlay mirroring compatible: iMac (Mid 2011 or newer), Mac mini (Mid 2011 or newer), MacBook Air (Mid 2011 or newer), and MacBook Pro (Early 2011 or newer). So if you have a machine from early 2011 or earlier — that's barely a year old! — you're stuck.
(Not that it'll make you feel better if you have an older Mac that doesn't support AirPlay mirroring, but FWIW it's not just a ploy to force people to get a newer machine: The short version is that AirPlay mirroring requires a graphics card with accelerated h.264 encoding hardware, i.e., Sandy Bridge chips or newer. The long version is this.)
It's a mark of how far we've come that a feature that would seem relatively niche — putting whatever's on your computer screen on your TV — can inspire so much anger. It's no longer a neat trick, or a feat that's the province of nerds: It's now kind of expected that you can beam stuff from your computer to your TV screen, totally hassle-free. Why can't you move things from one screen to another whenever you feel like it? It seems quite silly any other way.