While working on the pictures shot by various guests at my sister's wedding, I discovered two tools that helped me tremendously dealing with several problems I encountered: dcraw lets you mass convert the RAW formats of various cameras into JPEGs (or other formats). Obviously, for individual special shots it is nicer to use a RAW tool to achieve the best conversion results, but if you need to convert many files, this one is really helpful. EXIF tool lets you edit the EXIF data of a file or copy the EXIF data from one file to another (!) - for example, from a RAW file to the JPEG file created by dcraw. This helped with time-shifting the images where people forgot to set their camera's date and time.
Both tools operate on the command line. For Mac OS X, there's an alternative program that allows for shifting the time stamps that integrates itself directly into the Finder. I'd have to search for the home page of that one first, though.