*Ahem* I'm here to clear up an important misconception about the Japanese language. A lot of you people are calling yourselves 'mangaka' (or manga-ka or manga ka) without really understanding what that means.
A mangaka is a professional manga artist.

This means that, quite simply, if drawing comics is your hobby and you don't get paid for it, you are NOT a mangaka. You are a person who draws manga as a hobby. Even if you do manga or anime style drawings and earn money off those, you are not a mangaka, you are an artist or graphic designer who draws in the manga style, but since you're not actually making manga, ie. comics, you can't describe yourself as a 'mangaka'.
If you are making money as a creator of comics, then and only then are you an actual 'mangaka'.
Why is this important? Well, it was important enough for my Japanese sensei to give the members of our class calling ourselves that a telling off back in the second year of my degree course in the subject. I figure this means that she didn't want us going around in Japan in our year as exchange students calling ourselves 'mangaka' and embarrassing ourselves, our university and therefore indirectly her with incorrect usage of a term. It's basically the same as if in English you called yourself a 'Writer' when all you write is the odd internet fanfiction. Sure, you can get away with it casually, but if you want to sound like you know what you're on about, avoid using the term until you've actually made it. That way, the title means something.

....I'm bound to now get responses from a load of fanboys and girls saying 'but it's just for fuuunnn! It doesn't matter!' I would respond by saying, no, it doesn't really matter unless you're interested in not looking like an idiot. If you don't mind looking like an idiot, then by all means..