I have been a frequent QQ user for several years. I taught at a university in central China for a while, and have made many extended trips to China. I have QQ on my home and office computers, and my iPhone and iPad. The problem from a non-Chinese speaker point of view is that since version 2.2 they have not done the English language localization, so it is essentially impossible to use if you cannot read Chinese. It irritates me that the iOS version keeps pestering me to upgrade.
I give it some stars for being feature-rich, and improving, but the language issue is a deal breaker for the rest of the world.