Thanks to Mike for his comment on my earlier post about Snopes.com, which uses a JavaScript hack to prevent you from selecting text with the mouse. Mike points out that entering javascript:void(document.onselectstart=null) in the address bar negates Snopes's hack and allows you to select text again.

It'd still be nice (and probably trivial) to have Safari and Chrome extensions that do this. In the meantime, you can drag this "AllowSelect" bookmarklet to your Favorites bar. When you go to an article on Snopes, click "AllowSelect" and you'll be able to select text. This should also work for any other site that uses the same trick Snopes does.