I use a MS Access database that I wrote specifically for the purpose (in my case it's a 35mm slide catalogue). Every slide (worth keeping) is classified, assigned a unique reference number and key features noted by a system of "radio buttons". So, for example, I can search for images of the Yorkshire Dales that have snow, waterfalls, taken at night, with personal friends included etc. It was a chore to get this up to date but keeping it so is not too bad. Recent slides are scanned, thumbnailed and referenced to match the database. If I ever get a decent digital camera, the process will be a bit easier, I think. Be warned - it needs real discipline to keep up to date. Let it slip and you'll struggle to cath up.