I love being able to access a given tab by its number, and using 9 to mean "go to the last one". I often follow the pattern of "open new link in a tab and go to it at the end" and also have windows open with known apps up in the same tab location so I can get to them quickly, without even thinking.
Firefox does this by default, and WebKit/Safari does not.
I got this working on Safari and WebKit via AppleScript, bash scripts, and Quicksilver triggers.