Resolved questions
using あなた in conversations

hello, all this time i use あなた in conversations exactly just how i use "you" in english and i thought it will always be polite,
but i've just read in Tae Kim's guide (in grammar guide - essential grammar - addressing people) that using あなた can also be rude, and i actually don't have to use anything at all unless there's no way to address that person.
i think using 君 is kind of being too friendly. so i use あなた with every italki users in my messages, now i'm afraid that i may had been rude in some messages! >_<

so the question is: is this true? how rude can it be? i'm a girl, any other tips in addressing people?

thank you! ^_^