To add my 2 Rappen to this discussion: I have a company where I employ an assistant (or secretary to be politically totally and abysmally incorrect). Because I prefer a relaxed and more or less informal style of working, I used to switch to "Du" after the first few days. HOWEVER, my previous secretary was an absolute &&%%**** in all matters concerning precision, care and responsibility. This slowly developed after she'd stopped trying to impress when she was new on the job. Her English was good, but that was about it. Soooo, to cut a long story short, and after having had numerous talks in the nicest possible way about getting up to standard, I had to fire her. This is really difficult if you're on a "Du" basis with someone, believe me! That's why I've kept the "Sie" with my current assistant, even though she's worked for me for almost 2 years now. The style is still very relaxed and friendly, but the "Sie" helps when correcting mistakes or when asking her to do something. It gently and subtly underlines who is boss, even though in most matters it's no longer necessary.