EL COMANDANTE  SafariTabs 0.6.3 don't works anymore with the last release non beta of safari 4 (5530.17)  
(Version 0.6.3)

NEIL_M  @Chrisza

Read the requirements above;

Mac OS X 10.4 or later, SIMBL, Safari 4

Have you installed SIMBL?

In the time it took you to write your comment, you could have searched for it and installed it.

SIMBL - http://www.macupdate.com/info.php/id/18351/simbl  
(Version 0.6.3)

CHRISZA  Err, it says to install I must drag bundle to a SIMBL/Plugins directory.

No such directory on my new powerbook 10.5.6  
(Version 0.6.3)

SHANE C SMITH  Search for Glims, it will do this and so much more.  
(Version 0.6.3)

CALL ME YO DADDY  Sorry to crash the party but I was using Saft for better tab functionality before this came out. However a simple terminal command is all you need to make Safari's default tab functionality mirror Firefox and Opera's. This commands simply opens links in a new tab instead of an annoying window. Expert from MacUser:

You are required to launch Terminal (which can be found safely nestled within /Applications/Utilities) and enter this command:
defaults write com.apple.Safari TargetedClicksCreateTabs -bool true

Once you hit return and relaunch Safari, you’ll find that it will never steer from the noble path of the single window web browser now, no matter how trying the circumstances. The gates to ultimate web surfing joy will part and you and Safari will live happily ever after.   
(Version 0.6.1)

CHOLYWELL  The option to force links that open a new window to open in a new tab doesn't work with Safari 3.1.  
(Version 0.6)

ALEXIUSCA  Very promising, however it's frustrating that the plugin asks you if you want to restore, even when there are no windows to restore. Please make this a bit smarter!!  
(Version 0.6)

DRUMMIST53  crashes my MDD G4 Safari 3 every time..had to remove it..  
(Version 0.6)

LANOUVELLECHAIR  It's nice but it will be great if this plugin force windows to open in tabs too.  
(Version 0.5)

FFASS  Works fine for me. Running Safari 3.0.4 on Mac Pro, OS 10.5.1. Session history is recalled spiffily.  
(Version 0.5)