Excessive use of images or Flash animation on a page:

If your web page has plenty of nice-looking graphics and eye-popping Flash animation and not a lot of textual content it may indeed look nice but have you ever considered what how the search engines might see it. Search engines thrive on textual content, scavenging as much text as they can but unfortunately they cannot understand images or Flash animations like we can and so will find nothing of real value on your page. Try to balance your page so that the textual content is given priority and that any images or animations are used only when needed. Also it is a good idea to attach some text to an image by using its ALT tag as search engines use this text when determining rank.

Source: http://www.geocities.com/frakilk/seo-mistakes.html