Many commercial word processors are based on the WYSIWYG principle: “What You See Is What You Get.” LyX, on the other hand, is based on the principle that “What You See Is What You Mean.” You type what you mean, and LyX will take care of typesetting it for you, so that the output looks nice. A Return grammatically separates paragraphs, and a Space grammatically separates words, so there is no reason to have several of them in a row; a Tab has no grammatical function at all, so LyX does not support it. Using LyX, you’ll spend more of your time worrying about the content of your document, and less time worrying about the format.
No, I didn’t get it working on OS X yet, but working with it on FreeBSD is pretty fun. It’s about time someone made an editing tool that did most of the work . . . .