I’m generally a fan of tabbed browsing and make heavy use of it in Safari. You can set Safari to open a link in a new tab by holding the command key (on the Mac), but it won’t do this automatically, like when you click on a link that normally would open a new window. You can force Safari to do this by opening up the Terminal in Mac OS X and typing the following command:
defaults write com.apple.Safari TargetedClicksCreateTabs -bool true
You’ll have to quit and restart Safari for the changes to take effect. I just did it in the Safari 4 beta and it works like a charm.