I file the topic of usability in with design. Not something I often pay attention too.

Recent explorations into jQueryUI led me to discovering a great article on the subject of tab control design @ useit.com.  Jakob’s website is a treasure trove of articles all about useability in IT which make for good reading during downtime.

Is there some sort of standard or ruleset for web usability?

Another link I found: http://www.usability.gov/guidelines/.