This used to be fairly popular for a while for some bizarre reason as people thought it would prevent their copyright from being stolen. These days it mainly seems to show up on the odd art site or blog, most likely because its owners really don’t understand how easy it is to bypass.
Like most copy protection schemes, disabling right click annoys and harasses users while doing nothing to discourage anyone dedicated to lifting copyrighted content. Protecting photos and images is best done with watermarks and by registering your images. Disabling right click will not prevent your images from being lifted. Anyone who wants to badly enough can bypass any code based precautions with a simple screenshot.
As for protecting your written content, first of all it’s easily accessible in your source code, in the google cache or numerous other ways. The biggest problem with written content being lifted comes from blogs who syndicate other people’s content, rack up the keywords and cash in on the adsense or various cheaper Helium ripoff type sites that pay users to make their mini-wikis and are often stocked by Southeast Asians who lift the content, collect the cash. The solution there is Copyscape, not that there’s much you can do about them once you catch them. If you’re worried about this sort of thing, type up your material in a PDF file and lock it down, or turn it into a JPEG which would make it useless for keyword harvesting.