Here is a Safari Tip (or perhaps a bug?!)...
Open two different Safari windows, with one being the active window, and the other being the inactive window, and load two different sites. If you then Command-click on a link in the Inactive window, it will open a new tab in the Active window. The point being that you might expect a tab to open in the window that you are command clicking in, but instead it opens in the other window...
[robg adds: Some might consider this a bug, but I think it's a feature, and a side effect of OS X's treatment of command-clicks in background windows -- that is, that they are basically ignored by the window in which they were applied. This is how, for instance, you can change your iChat status without bringing iChat to the foreground - just Command-click on the Status line. So in Safari's case, the command-click on the background window is executed, but the results are then sent to the active window.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040415122719935