John Gruber first points out that Safari always places new tabs on the rightmost side of its tab list. He then elegantly walks through the process of getting Safari to create new tabs just to the right of the current tab.

It’s not trivial, but definitely interesting and worth the read. Even if this particular tab issue is not a problem for you, knowing how to create a script and assign it a command-key shortcut that overrides what’s built-in has lots of value.