I haven't tried Duolingo with a language that I hadn't previously studied, but I can see how it would be easy to be totally lost. It offers very little explanation of what's going on; you just have to pick up on the patterns (or already know some basic grammar).

Have you tried tinycards for vocabulary? I'm having fun with them as well.

And wow, Arabic? That must be a very hard language to learn. The alphabet alone looks crazy difficult!

I am enjoying the language-learning through music, and appreciating how all these songs are up on youtube, especially as I can't find them at the itunes store.