There are still some purists in the world who feel that every website should be viewable on the widest range of computers, including really old ones with unfashionably slow modems, simple browsers and no plug-ins. And funnily enough this argument is strengthed as the range of devices on which you can view websites broadens to mobile phones, games consoles and cheap palmtop organisers. These new little gadgets can't always deal with the flashy multimedia web stuff which can look cool on fast PCs. So the people saying "We want all websites to work on our ancient big technology!" have been joined by people saying "We want all websites to work on our new micro technology!". Ah, the circle of life, or something.
At the other end of the scale, there are those people who think that as soon as any new browser plug-in is released it must be deployed in the most ridiculous way possible, or as long as at least one person they know has personally tapped into an internet trunk route with a huge cable then it must be the time to start sending full-screen feature films instead of their previous 'Hello!' home page.
Sanity, of course, lies somewhere between these two, but probably closer to the 'pure and simple' model than the mad show-off one.
You can have perfectly nice websites that have ordinary text plus a few carefully-crafted ornaments. Let's face it, as long as they are well-designed and have decent content, sites like that are unlikely to annoy you. Whereas the chances of you being annoyed by having to sit through an inescapable stupid animation and listen to a noise and to wait while lots of things load is quite a lot higher.
Of course, there are some 'heavy' multimedia sites that have been slaved over for months by intelligent perfectionists and are absolutely brilliant. But everybody else would probably be better off keeping things reasonably simple.
Having said that, I only recently discovered that making animations in Macromedia's Flash is quite simple (I mean that you would expect it to be more difficult to pick up than it is). You can produce big-size graphics with very small file sizes, like the one below which is less than 10K. And Macromedia have a 30-day free trial version, so you can try to make all your Flash animations in 30 days and not have to buy the thing. (This is not as naughty as it sounds. Macromedia benefits from the proliferation of Flash on the web anyway -- yes, you are helping them).
Even so, these things have to be used in moderation. Reflect on this as the animation below makes you dizzy.