This is an easy one. Hiding the current application with Cmd-H is sometimes convenient. But getting rid of everything else but the current application, now that's convenient! When you've got all sorts of *junk* behind and beside your current window, clean it with Cmd-Option-H. Gone!!! For a very long time, there was no keyboard equivalent for *Hide Others*.
By the way, I was reminded of this tip while reading Anandtech's first Macintosh trial. Anand calls it: A Month with a Mac: A Die-Hard PC User's Perspective. Considering that Anandtech is one of the best PC websites on the net with 5 million readers, the report is surprisingly positive. Anand doesn't call himself a switcher since he continues to use PCs as well, but he is a daily Mac user now with his 2 gb dual PowerMac and Cinema display at the ready. Since this report on October 8th, he's created a Mac section to Anandtech which I will be following. There's a part II to his Mac story that is about a Powerbook and more recently he's written about the Mac mini.