When was the last time you found a site that contained music and actually enjoyed the experience? If you can think of any, it's probably the exception rather than the rule. In general, the only time music should play on a site is when you are visiting a music related website. Your favorite band can play their latest song on their site, for example. But that's pretty much it.
If you have to have music on your site, let the visitor have complete control over it. This cannot be overemphasized. A fundamental rule of the Web is that the site owner is not in control of the experience -- the visitor is.
See the last point. People hate to wait when they're using the web. Anything that slows their access to the information on your site makes them that much more likely to look elsewhere. How many brick-and-mortar stores would put a TV in the doorway to the store that customers would have to step over to enter?
Blink and they miss it
Blinking text on websites went out a long time ago. But there are contemporary equivalents in the form of distracting animations and poor color choices. These things show that a site owner hasn't invested time and effort into his Web presence. Since people judge a site's credibility within a few seconds of seeing the page, this lack of attention says that the business doesn't care about the customer experience.
In spite of the previous points, there is such a thing as too much choice. Don't make visitors choose between Flash and HTML content, or select a "printer-friendly" version of the page. Modern Web design allows stylesheets to be specified by media type, so print formatting should be completely transparent to visitors.