The first to two years I took digital photos, my meta data was messed up by my camera software, due to this I store the first couple of years as folders named by the people on on the photos.

Since 2003 I store my images in the following structure:
{Year}
{Month}
{Day} (And in some cases a description)

This is what my folder for December 2009 looks like:

2009
12
02
05, En tur til Sverige
17, Cirkus på skolen
20, Besøg hos Uffe og Maj-Britt
24, Juleaften
27
28, I Zoologisk have

How do you store your images?