I agree.  I kept a journal of our England trip and it is very enjoyable to go back and relive the many experiences and funny happenings.  Also, it comes in real handy when arranging pictures while scrapbook.  My mother constantly calls me to ask "What day did we vist this or that?"  

This is an excellent idea, because it also helps when sorting through photos that you've taken.  I used a small spiral bound notebook that fit into my Go Ahead bag or purse/backpack.  I filled out tour and hotel info before the trip also and jotted down hotel room numbers as we went along our trip so I wouldn't forget.  The other thing I brought with me and I am still listening to -a small microcassette recorder.  I tape recorded our Tour Director on the bus, I recorded some of the tours we went on through castles, museums, Abbeys, etc. and I just sat the recorder on the dinner table that picked up conversations and dinner entertainment.  I marked the cassettes in numerical order so when I re-listen I can do so in the order of the trip.