Since I first mentioned Magic Lantern, I receive quite a lot of questions whether it is really safe. I'm using it for more than a year now (almost 1.5 I think) on both my bodies: 50D and 5D MK II. In previous version I had some small issues. Restarting a camera was all that was needed to "fix" them though. With latest release, that is 2.3, I haven't run into any problems so far. It runs perfectly for me and is invaluable addition to my photography workflow.
You must be aware though that there is no bug-free software, it's one of the fundamental rules of software development. Through testing number of bugs is minimized but they are still there (hidden somewhere, waiting for a moment to attack ;) ). Even systems which are expected to be completely free of the issues (like computers in airplanes or in military systems) aren't always. There were cases in the past where for instance a missile hit wrong target due to "small" error in its software... I'm telling you this as a developer myself. It doesn't mean that you shouldn't try Magic Lantern (I would say you have to in fact) but there might be cases when something won't work as expected. They should be pretty rare but I can't guarantee everything will be ok, especially as I'm not developing it :)
Summing up. In my opinion Magic Lantern is safe and is a really great piece of software. It's used by thousands of users out there (including professional photographers) so the chance you will have problems with it is very very small.
You can download Magic Lantern for free here.
Today photo is a fake tilt-shift created in Photoshop CS6 using its new tilt-shift blur filter. I used this HDR photo as a base.