When you're approaching the design of your site, it's apparent that technology is king. Web designers will tell you that selecting the right platform to build your site can make a huge difference to its look and usability. As a consequence, many sites are built using highly complex technologies, filled with all sorts of bells and whistles.
Then the site is considered from a search engine optimization perspective. Under this new gaze, not only are the bells and whistles too much noise, but the technology platform the site is based upon is sometimes a liability. What site owners usually come to realize is that they would have been better off working from the basics, focusing on the best they could do with HTML and text.
When it comes to search engine optimization, it is clear that text rules. This is because of the way the search engines trawl the web. Search engine crawlers have become increasingly sophisticated over the years, but their bias is still toward the format they began with, namely text. If you can fit all of your content into text within plain, text-based code, there's a higher chance that the search engines will understand your site, making indexing a little easier.
A solely text-based site is not entirely attractive to your human users, and there must be some balance. At the same time, your SEO work will be cut in half if your site has nice, handy chunks of text to work with.
If your site is built entirely out of Flash, don't despair. SEO companies are able to work around Flash and other not-so-SEO-friendly technologies, and Google is constantly trying to improve the algorithm's relationship with web design technology. It is important, however, to be aware that the task isn't going to be easy.