Mac only: Get a dynamic list of recently accessed files using Smart Folders in OS X. MacWorld magazine explains how:
Create a smart folder in the Finder by selecting File -> New Smart Folder, or by pressing Command-Option-N. You'll see two lines of criteria in the folder. In the Kind criterion, select Any, or, if you want to limit it to documents, select Documents. Set Last Modified to Since Yesterday, or if you want to go back further, Within Last N Days, where N is the number of days you want to use.
Click the Other button in the location bar, then click the plus (+) button to add folders.
A "Recent Documents" Smart Folder is a great one-stop access point for files you're currently working on but that are located in different "actual" folders. Here's how to save searches as folders in Windows Vista.