And if you use these to draw attention to something adjacent to them, such as text, their mere presence will be extremely annoying when the reader is trying to read what you want them to read. Background graphics is another way for coolness to interfere with your website. Most backgrounds, even lightly textured ones, reduce legibility of plain text. Solid colors that contrast strongly with text colors are really the only way to ensure legibility. It should go without saying, but there are some really hideous backgrounds on the web that totally destroy their pages.
Understatement works surprisingly well on the web.
Remember that when your page comes up, your reader will be completely focused on it. So know what it is that you want to say, then say it and be done with it. If you've done your job well, you'll get your point across. If you haven't, no amount of cool is going to compensate. There are a lot of things that go into this, more than some of the really awful sins.