John Gruber, on Daring Fireball, detailing how he got to change Safari’s behaviour to open new tabs next to the active tab:

If I have, say, 10 tabs open in a window and I’m currently using, say, tab 2, when I type ⌘T to open a new tab it feels like the rightmost end of the row of tabs is “way over there”, but what I want is the new tab to open “right next to where I am” — like what happens when I ⌘-click a link.

A few months ago I asked on Twitter if there was a secret preference in Safari that would change this to what I want — which is for new tabs to always open right next to the current tab. There is no such preference. I set about trying trying to figure out if this could be done using AppleScript, but I couldn’t figure it out.
Jeff Johnson figured it out, though, and was kind enough to share the solution and explain the rather ungainly syntax required.

John used FastScripts for this but I decided to try my luck with Keyboard Maestro…

This was extremely easy. I added a new macro to my Safari group (macros limited only to Safari), used ⌘T as the Hot Key trigger, which will override Safari’s action, and just pasted in John’s AppleScript:

tell application "Safari"
    tell front window
        set _old_tab to current tab
        set _new_tab to make new tab at after _old_tab
        set current tab to _new_tab
    end tell
end tell

Works like a charm.