Validated code is also important.
To be honest, most webmasters don't worry about validating their code as often as they should. Running validation through a service like: http://validator.w3.org/ is a great way to make sure that your website is readable by the search engines.
Validated code means that all the stuff that goes on behind the scenes is laid out the way it should be. If it's all good, the spiders don't miss things.