The Gadgets Page has some great tips on ensuring that your digital photos don’t disappear or get lost.
One tip they note is to rename your photos to keep track of what they mean. I recommend the Flexible Renamer as it uses powerful operators and makes renaming large quantities of photos a snap so I can add the date from the exif information and add other information like location, keywords and titles to the filename. Sure the filenames are long but it’s much easier than manually assigning keywords in Picasa.