MACINSETEX in safari 3.x, right click or ctrl-click in the tab bar produces a contextual menu, "New Tab."
Don't remember what occurred in Safari 2.x as i usually invoked Command-T to open a new tab.
I suppose double clicking the tab bar would save a person a few milliseconds per incident. Additionally, having the double-click-on-tab-bar to produce a new tab, in safari, could preserve a few brain memory cell because the command is used across all browsers.
Okay but...
(Version 1.2.1)