If we wanted to be picky about it, we'd say 404 pages are not errors and can even be (blasphemy!) an acceptable user experience.
Facebook, Google+ and Twitter can help make your content more shareable with rich snippets of content that can be shared across platforms.
This article will outline the appropriate SEO method for handling product versions, colors, sizes and variations on ecommerce sites.
Our in-house test of iframes and how search engines treat content and links found within them. Google does appear to be following the source calls found in iframes and passing equity, but seems to be the only search engine doing so.