Predictable design
Jonathan Snook just posted a nice example of why you should stick with what's predictable. When designing, there's a lot of temptation to go against the grain, to do something a little different than everybody else does it. Except, it makes your interface less predictable. And predictability is key for user friendliness. Whether it's underlines on hyperlinks, or simple navigation titles, you'll usually end up winning more points for usability than you ever will for creativity.