Forum Moderators: phranque
1) important text content in presented with graphics.
2) flash only site.
3) a site that uses a JS sniffer, and redirects to a splash page when JS is not supported.
Any of those will pretty much guarantee poor results in the search engines, but the list is pretty much endless.
* Cloaking (some people would add: "unless you *really* know what you're doing");
* Changing the structure of your site dramatically without creating the appropriate redirects (301);
* Link hoarding to "preserve PR";
* Excessive cross-linking between your own sites.
Then I would add anything that puts off the visitor:
Anything flashing and scrolling; popups / pop-unders, "free" hosts that smear cr** all over the page ..
Anything that looks amateurish: garish colors, mis-spelled words (sp?) . .
Large hit counters that look like 'Visitor # 000019 '
Validate pages to find dumb small things which could prevent proper indexing.