It's an idea that makes so much sense. Buy a movie, and get a digital copy inside the box for your PC or iPod, so you don't have to go through the hassle of ripping/torrenting/pirating a copy for when you're not in front of the TV. But the simple truth is that every movie studio has a different idea of exactly what a digital copy means, despite almost universally using the "digital copy" terminology. So to help, here's how digital copy is implemented by each of the studios:
20th Century Fox
Fox have got the digital copy thing down. Inside your Blu-ray purchase is a DVD, which includes a copy of the movie or TV show in formats for both Windows and Mac (or more specifically, iTunes). They're both DRM'd up the wingwang, so forget about piracy - or even sharing with your friends. You need a special code (also in the box) to activate the digital copy, but after that, you're cheering.
Fox offer digital copies in both the retail DVD and Blu-ray versions of the film, with titles available including the Ice Age trilogy, Night at the Museum 1 & 2 and the upcoming Family Guy Star Wars spoof, Something something something Dark Side.
If you want to watch digital copies of Sony movies on your iPod or iPhone, then you need to go out and buy Terminator Salvation on Blu-ray. Because the guys at Sony Pictures Australia are using it as a test bed for including an iTunes version on the Digital Copy DVD. It too will have more DRM than the Terminators had the chance to actual kill John Conner in the movie, but it's a huge step forward.
Other than that, the original Twilight film had a digital copy, although it was PC only and technically a Hoyts film distributed by Sony Pictures, rather than a Sony Pictures picture.
Roadshow are a Windows only kind of Digital Copy operation. They've flipflopped on their approach to the feature as well – Zack and Miri make a Porno had a bundled DVD with the film on it, while 17 Again, Four Holidays and My Sister’s Keeper are all downloaded from the net using a special product key in the box. Standard DRM limitations apply, but you didn't expect anything different, did you?
Upcoming Roadshow films with a digital copy include The Final Destination 4 and Time Traveller’s Wife.
Warner's also got a Windows-only, at least at the moment. While the US Warner titles come with both Windows and iTunes versions, in Australia, we only have access to download the Windows version. And it is a download - enter a code and get your DRM-lined copy through the Interwebs.
Warner's got a pretty extensive range of films with Digital Copy - including all the Harry Potter films (although not every release of every film) plus RocknRolla, Body of Lies, The Curious Case of Benjamin Button and The Hangover.
Paramount believe in OS equality, offering versions for both PC and Mac via iTunes. The digital copies are stores on a bundled DVD, have the same boring old DRM I've mentioned half a dozen times already.
So far, Paramount have only released a couple of films with the digital copy: Star Trek XI and Transformers 2. At least they're both geeky films...
Disney's Digital copy mechanic - dubbed DisneyFile - includes a bonus DVD in select Disney films which contains both a PC and Mac copy of the film in SD for your personal consumtion, either through Windows Media Player or iTunes (and subsequently iPods). The thing about Disney's iteration is that it has a simple software program to guide you through the process.
So far, the only Aussie Disney release with the copy is Hannah Montana: The Movie. Not really your thing, I take it?
At the moment, Universal don't actually have any local releases with a digital copy, although that could change in the future.
It's important to note that this is only for Aussie releases. A quick look at the Warner digital copy website, for example, shows that in the US they offer both PC and iTunes copies of the film, while some markets also have DVDs included in the box.