In light of the interest attracted by the previous post, and of several discussions I've had about this topic in real life lately, I'll be posting regularly (?) on a few of the several myths widely believed in Algeria about Algerian Arabic, and often elsewhere about other Arabic dialects.
1. "Darja has no rules."
Every language has rules. You can see some of these rules in action by examining the effects of changing word order: for example خالد شاف روحو (khaled shaf RuHu - Khaled saw himself) is perfectly fine, but خالد روحو شاف (khaled RuHu shaf - Khaled himself saw) is totally bizarre. This is not because of some inevitable law of human thought: in Japanese, "Khaled himself saw" would be the correct order. Likewise, ما شفْتْشْ الطّونوبيل (ma sheftsh eTTunubil - I didn't see the car) is fine; شفتش ما الطونوبيل (sheftsh ma TTunubil) or ما شفت الطونوبيلش (ma sheft eTTunubilsh) are ridiculous. أنا راني نكتب (ana Rani nekteb - I'm writing) is fine; حنا راني نكتب (Hna Rani nekteb) or حنا رانا نكتب (Hna Rana nekteb) are absurd. If you speak Darja, you'll be able to see this instantly, even though no one ever taught you that one was right and the other wrong, and even though all of them would be wrong in FuSHa. The difference between Darja and FuSHa is not that FuSHa has rules and Darja breaks them; rather, Darja has different rules, and, whereas the rules of FuSHa are usually learned at great effort from teachers who learned them from grammar books written hundreds of years ago by people like Sibawayh who themselves had to go and spend hours in the desert with the few Bedouins who still spoke "proper" FuSHa, the rules of Darja are usually learned unconsciously from your own parents and relatives and followed effortlessly from the moment you're old enough to talk - as those of FuSHa were back in the 7th century when some people still spoke it as a mother tongue.