One of my pet hates is using IFRAMES on a web page. The content of the IFRAME is inviisible to search engines and doesnt help at all with Search Engine Optimisation efforts.

IFRAMES, FRAMES and JAVASCRIPT navigation have inherently caused problems for webmasters because most search engines are unable to parse the content of these sections, not forgetting of course that small percentage of web users who are dedicated to surfing with JAVASCRIPT and IFRAMES disabled.

With a bit bit of forethought all these problems are realtively easily to overcome. For example by using the <NOFRAMES> </NOFRAMES> tags in a FRAME page and similarly a <NOSCRIPT></NOSCRIPT> tag appended to JAVASCRIPT Navigation, relative content and links could be fed to search spiders and non scripted browsers.

Likewise with IFRAMES. Search spiders will happily read anything between the <IFRAME> and </IFRAME> tag. So instead of showing search engines and the odd websurfer that lame old "This option will not work correctly.  Unfortunately, your browser does not support Inline Frames"  message, liven up their world with good Links and relevant content.

Personally I treat the area between the <IFRAME> and </IFRAME> tags as a valuable resource for additional SEO on a page. ie. Keyword loading, additional content and additional links.

In reality the perfect scratchpad for serious SEO in a section of a web page that browsers dont normally reproduce.