Overview
Hi, I came here after doing a search and the tip about Mac DVD Ripper Pro worked for me. I can see lots of little bits of info in this thread and some confused readers, so for those who might be having trouble piecing together all the info here, I thought I'd put together an overview. Hope this is helpful.
First, there are two ways to "rip" DVDs. One way copies the entire disc (minus the CSS copy protection) and the result behaves like an actual DVD. You can access menus, special features, sit through the FBI warnings, etc. The main downside is that the resulting files are as big as the disc itself--typically 4 to 8 GB. Programs like RipIt and Mac DVDRipper Pro do this.
A DVD itself is nothing more than a data disc with a folder named 'VIDEO_TS' which contains all the movie data. RipIt will create a folder with these files and if you launch OS X's DVD Player and choose File -> Open and navigate to this folder, it will play just like an actual DVD. (Or you can name the folder with the '.dvdmedia' extension and double-click it and DVD Player will automatically launch.) Mac DVDRipper Pro creates a disk image (.ISO file) and if you double-click on it, a virtual disk will appear on your desktop, and if you open it you will see the VIDEO_TS folder. This, too, can be played with the DVD Player app.
The other way to rip movies is with a program like HandBrake. This program converts one part of the disk (the movie itself) into a single video file (MP4, AVI, etc.) and it is compressed (like an MP3) but it is nothing but the movie itself--no menus, special features, etc. The nice thing is that the files are smaller--typically from 700 MB to 1.5 GB for a typical 90-minute movie (depending on the quality settings used--again, like an MP3 at 128kbps or 192kbps, bigger files look better.) And if you want to just watch the movie it's great--it opens instantly like any other QuickTime movie with no DVD menus, previews, or notices to wait through. You can also load these files into iTunes, watch them with FrontRow, play them on an iDevice, etc.
Unfortunately, unlike audio CDs and MP3s, NONE of this is legal in the U.S. (The ripping itself would be illegal, except the info on the DVD is encrypted, and breaking the encryption is illegal. That's why iTunes will rip CDs but not your DVDs.) Movie studios use a variety of tricks to keep people from copying discs, and it's a cat-and-mouse game between the makers of DVD protecting software and the makers of DVD ripping software. At any particular moment, any particular disk may or may not be rippable with any particular piece of software.
For the current case (Thor), neither HandBrake nor RipIt work (as of mid-September 2011) but Mac DVDRipper Pro (even the free-for-five-rips demo version) can. It's very simple: stick the disc in and you'll see something like this:
http://pixelcity.com/dvd/dvd1.png
(Different movie, same message--I didn't think to grab screenshots when I was ripping Thor.) When you click "Rip" it will show you a message like this:
http://pixelcity.com/dvd/dvd2.png
Go ahead and accept its suggestion of "Switch to full disc mode" and it'll work.
Still, more remnants of the copy protection remain. The ISO will be the same size as the DVD (about 7.5 GB for Thor) but if you open it and get info on the VIDEO_TS folder, the computer thinks it's over 40 GB, and if you try to drag the folder to your desktop, that's how big it'll be. It will work just fine, though. Double-click the ISO, launch DVD Player, and you're in business.
If you want to rip it and compress it to a single file with HandBrake, there's one more obstacle. Content providers try to make them hard to rip by making it appear that there are 99 "titles" (which are like "tracks" on an audio CD) on the disc but that's actually pretty easy to get around. With the ISO mounted, launch DVD Player (and put it into Windowed mode if it's full screen.) Start playing the movie--get past the menus and into the movie itself. On the app's simulated "remote" screen, click the word 'TITLE' (it doesn't look like a button but it is) once or twice and it will show you which "title" is being played. As others have mentioned, on this disc it is #24 out of 99 tracks. (Shown on the display as "24/99") If you rip any of the other titles you'll wind up with a bad video file--scrambled or missing scenes, out-of-sync audio, etc.
The fine folks who make RipIt will eventually update their software to work with the newest crop of discs. (They are constantly doing so.) One nice thing about RipIt is that they do some of this work for you: if you rip the disc (once they get it working) you'll wind up with a VIDEO_TS folder that is the correct size, and if you then try to rip that with HandBrake, only the correct title will appear in the list, saving you the step of figuring it out for yourself. But, as with anything else, it's good to have more than one tool in your drawer for occasions such as this.