I have never been an avid fan of Safari because the browser stinks. But after I checked out Safari 4, I noticed its speed and how it handles its resources basing on the performance when I use the browser to surf sites. Even until now though, they still do not provide the option to set Safari to open sites in a new tab instead of a new window.
I know, pretty annoying right? You are doing something, then once you click on a link, all of a sudden a new window pops up instead of a new tab. What is the point in producing a tabbed browser if this option is not provided. For Mac OS users, there is a way to do this but it is not within the browser.
You would have to open the Terminal program located in Applications > Utilities and type the following and press enter.
defaults write com.apple.Safari TargetedClicksCreateTabs -bool true
That is all. Restart your Safari and you should be getting those new tabs that you so desire.