To open links in background tabs should be the default behaviour. When opening a link in new tab it is normally done because one wants to continue reading on the current page.

For example:
Browsing through a search result page and opening a number of the resulting links that looks promising.
Or a forum index and opening all threads which are of interest.

Thus, opening links in new tabs without hiding the active one gives the most effective browsing experience.

(edit)
Another very nice thing is if the pages, which are opened in the background tabs, are loaded in background and ready to read when one switches over to them.


//j