I photograph my odometer too, using my camera phone. Sometimes I send the picture to my work e-mail address (where I do my online expense reports), sometimes I just save the photo and look at it on the phone when I fill out my reimbursement.

Another thing I do is call my office phone and leave myself a voice mail. I mainly do this for other reminders, though. I like the camera phone for the odometer.

Off topic, but camera phones are nice for price checking (photograph the sticker on the shelf). Also, you can take a picture of your hotel room number before you go to the bar. As long as you remember that you've got it in your phone, you'll go back to the right room!