It's especially handy when you're on the run and don't have your printed dictionaries with you. I'm often on the web while on my iPhone, and it works great there (or any other modern phone that has standard web browsing capabilities).
Not only is it easy, but it also has modern terms like 'computer', 'mobile phone', and 'gay', that your old printed dictionary probably couldn't even conceive of!
Also, you can download the whole dictionary as a single PDF. And you can contribute new words yourself.
That being said, it has its limitations. It won't conjugate a verb for you, for example, and the list of words is somewhat small. However, as the author states, it's not really meant to be a complete replacement for a printed dictionary. You still need that.
But when you're on the run and need something quick and dirty, it's a great way to expand your vocabulary. And if you want to add words or help validate them, there's a link on the site to participate.
And when you participate, you learn!
