Note: This tip is Leopard-only, sorry Tiger holdouts.
The Command-? trick is easily one of my favorites among the less-ballyhooed feature expansions of Leopard. If you missed that one, it allows you to search for menu items in any application by pulling down the "Help" menu, which can be triggered from the keyboard with the Command-? (Command-Shift-/) shortcut. Typing the first few letters of the menu item you're searching for will highlight its location in the dropdown menus. I use it a lot, but somehow missed one great capability noted by TUAW reader Maarten: in Safari, the menu item search extends to your bookmark collection and Safari history!
Because the bookmarks and history items are contained in the menubar's menus, they're searched along with the other menu items, allowing blazing-fast navigation of the sites listed in the Bookmarks and History menus. I like speed; I have my bookmarks toolbar set up with numbered titles which correlate to their Command-number shortcut (the first non-folder item in the toolbar can be accessed with Command-1, the second with Command-2, etc.), and I have keyword shortcuts assigned to my other most-accessed bookmarks using various tools. There's only so much room in my life, however, for organizing bookmarks and assigning keywords. History search can be a tedious prospect, too, even using Spotlight or Safari's History menu hierarchy. This trick provides instant search and it's only a keyboard shortcut away. Because the History results are sorted into sub-menus named by date, the results from the history menu appear with their access date first, so it's easy to navigate the results to find what you're looking for.
The concept behind this tip applies to all kinds of applications. I started experimenting and found that the search bar in the help menu almost always included recent documents and open windows ... basically anything the application lists in its menus. The bookmarks/history search works in most other browsers, too. I use Firefox as well as Safari, so I was happy to find it worked there, with one minor caveat: the Command-? shortcut in Firefox opens the Firefox Help webpage, not the Help menu item, requiring a mouse click to focus the search box in the dropdown. I haven't found a way to add shortcut keys for top-level menu items in System Preferences, so if anyone knows that, or another way to access the search menu via a shortcut key, I'd love to know about it.
Happy searching, and a big thanks to Maarten for the tip!