After a year with Leopard, I finally decided to look at the Spotlight search field in Open and Save dialog boxes, and I noticed there's a way to make application-specific sidebar items. I haven't seen this documented anywhere, though that may be because I get the impression few people use the Spotlight field in Open and Save dialog boxes.
Setting up app-specific saved searches can be useful if you have certain files or folders you frequently access from within a certain application. For example, I find most of my Photoshop work only goes into a couple of folders, and the same is true for my InDesign files, and web pages I save as PDFs.
From the Open or Save dialog in any application, enter a term in the Spotlight search field. If desired, use the plus (+) sign button to add criteria to your search (the Kind field can be very helpful here for narrowing the search results). When you click the Save button, name this Smart Folder and click the checkbox marked 'Display Smart Folder For This Application Only.'
From now on, you'll see your saved search in the sidebar of the Open and Save dialog within that application. For my tastes at least, the added bonus of these sidebar Smart Folders is that they are not displayed in the sidebar of Finder windows.
Should you later decide to remove one of these items, simply view an Open or Save dialog box in whichever application you wish to change, then drag the unwanted Smart Folder from the sidebar, just as one would in the Finder.
[robg adds: I'll admit to never have tried saving a search from an Open or Save dialog, so perhaps others have overlooked this useful feature as well.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090222210441370