I do Arabic course in livemocha and i have so good experiance.Arabic people are very helpful there and they always correct my writings and my speaking :-)
I'm beginner but i think there are so good lessons.Unfortunately there are not grammar explanation but the native speakers always help me if i have any question :-)
It's a good site and i hope i will finish soon the beginner courses :-D but i have to study a lot to reach my aim :-)
In my freetime i try to learn new words, sentences but the first is the English because in May I have my final exam :-)