I do something similar to Carl. I name the windows folder to match the set of pictures. Eg. "20080515 Kid's 13th birthday party". Notice I put the full date in the folder name in year/month/date format. This way the folders are sorted by age. I have master folders for each year, so I can more easily find and archive photos. I don't mess with individual picture names though. I'm a bit lazy that way.

The next layer I use is Google's Picasa program. With the number of pictures I currently have, it's just as easy to visually scan the photos as it is to enter key words and later do a search on the key words. Picasa will let you add comments to a photo. I'm not sure if they are searchable.

I have a free download from Microsoft called Photo Info. I don't use it much, but you just right click the photo and enter keywords. I believe these are stored in the file itself. You can select multiple photos and add the same keywords to all of them in one shot. By the info I see in the program, these keywords are searchable but I haven't tested that.

There are various photo sorting programs out there. I'm leery of any that keep the keyword info in a separate database. Move the photos to another computer and all your sorting work is lost. Did I say I'm a bit lazy? I hate doing things twice.

Bottom line, I do all my work naming folders and dragging the pictures to the correct folders. It won't help if you are trying to name everyone in the photo and later press a couple keys to show all photos somone might be in. My system means I do more work at the time I need the pictures (scanning them in Picasa). Also, my system requires someone who knows the people to be able to find the right pictures. Obviously, this isn't a good historic record.