The big problem with using it as a free portfolio site is the whole migration thing. I have to move everything here from facebook... And as someone who really doesn't care if people find out I'm a bit strange in the head (people in general don't much care I've noticed) the split between personal and public is kinda strange. BUT the greatest upside is the twitter feel of it. Its not like, for example Neil Gaiman would add me on Facebook, he doesn't know me, why should he bother? I still want to read the things he write though.
Here, best of both worlds. While I can write and comment he can still keep me well out of what he doesn't write publicly. Hopefully someone will see what I write or draw and think "hmmm what a lovely man, we must hire him post-haste! Give him money, tequila and fast yachts - the only way to make an illustrator feel at home!"... or something like that, the last part may be changed to "What a dope, lets hire him for tiny amounts of cash or preferrably fruit!" :)