I'm not sure how useful this is, but I just discovered that if you have more than one Safari window open and, if you hold down the Command key and click on a link in a background window, the link opens in a tab in the frontmost window.
This is an interesting twist on the Command-click to open link in a new tab shortcut in Safari.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061027030208781