Heres a curious announcement of a soon to be released Homebrew app at the Neoflash Contest, basically use your DS as a pedometer:

Hello all....

I'm going to submit a pedometer for the DS called sDepS. It will be of no use without an accelerometer. I'll link to the app here before deadline, but it's not quite ready yet.

The website is here: http://sDepS.wordpress.com

sDepS is a pedometer keeping track of your level of activity. Steps are registered as walking or running, and the total time spent on each type of activity is shown as well as the Steps Per Minute.

If you have one of the R6 products, please get in touch with me if you could test compatability.

Good luck to you all