I've tried many times to get past the beginner stage of learning Mandarin. Over the years internal and external distractions have kept me from progressing beyond what I'd call upper elementary level.
Now, I'm taking my efforts to the next level by enrolling for the three-year full-time bachelor "China Studies", starting September 2012.
I'll be very curious to see how iTalki works out for me. I've heard very positive stories about the general atmosphere here. I use other tools as well to help me master Mandarin Chinese: I'm a very avid user of Skritter.com, I've signed up with ChinesePod.com and I use a number of iPhone apps, of which Pleco and Flashcards Deluxe really stand out.
Other than my native language Dutch, I'm fairly fluent in English. I can also work my way around in German and French. In the distant past I studied classical philology (Latin and Ancient Greek), also at Leyden University.