OS X 10.5 now allows you to add items to the Finder's sidebar via drag/drop (to the SHARED section) from any Open/Save dialog box. This can be a real timesaver if you're, for instance, temporarily using one folder for a project. Drag it to the sidebar the first time you save, then have fast access to it for future files you add to that folder.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071028201246437