I find that Shih Tzus tend to annoy me in general. I find it hard to put my finger on what it is I don't like about them, but I still don't like them.
I'd just like to say DITTO on pretty much ALL of the advice given on this thread, there's some really good stuff here.
I agree with BP about dominance, in fact, I much prefer a dominant dog.... dogs that are too submissive usually have fear issues, not to mention the submissive urination.