It totally depends on the YOU and the situation.
Generally, it's said rude for your higher ranking person, such as your boss, but for example, when your wife calls you as あなた with sweet voice, it's so sweet. And when she calls あなた with violent voice, it's scared... How bad things did you do to her? lol.
In the conversation, it's easy to know our feelings with tones. In writing, it's hard, so we likely use smileys. (^ ^) To avoid misunderstanding, we omit YOU very often. I would say すみません、おなまえは？ or あのーなんとおよびしたらいいですか？
すみません、えーっと、あのー help to make the words mild. Short and direct words are sometimes too strong. なまえは? is simple but rude to your boss. おなまえは？ is not so bad if you are a woman, but it's so weird if you are a man. It depends on the situation...