We organize them by event.
Each vacation gets his own folder and also each event gets his own folder.
In those folders we have seperate folders for the different moments.
Like for our vacation this April we have a folder April 2011 then subfolders for before ABD, the ABD trip, after ABD and the WDW part.
Then in the before ABD folder we have again subfolders for each date.
For an event like a meeting we have just a folder for that event and then all the photos.
But for an event like a birth then the folder gets the name of the person born and then a subfolder (with the date) for each time there are made photos.
We store the photos on 3 different places.
The computer and also on 2 different external harddisks.