NEPRO JAPAN published in January 2004 the results of a study into people's useage of their mobile phones' GPS function in Japan.
At the moment, AU has more than 15 GPS-enabled models, Docomo has 2, none for Vodafone.

Below are outlined the results of the survey.

Of the 5654 people interviewed.
Female: 61%
Men: 39%

Age class.
under 10: 9%
20's: 45%
30's: 35%
40's: 9%
50 or above: 1%

Do you know what a GPS is?
yes: 68%
no: 32%

Are the GPS functions useful?
yes: 49%
no: 9%
don't know: 42%

How often do you use the GPS in your phone?
Frequently: 1%
Occasionally: 6%
Almost never:6%
Never:5%
Don't have one: 82%

Would you like a GPS in your phone?
Yes: 29%
No: 17%
Don't know: 28%
I have one: 26%

What single service would you most prefer to be offered with the GPS? (choice given)
Area daily life + entertainment infos: 16%
Area traffic infos: 16%
Lost phone recovery: 19%
Road guide, Navi: 22%
Emergency location: 20%
No preference: 7%

What services would you use? (free answers)
Location check for myself, familly and friends: 44%
Road navi: 21%
Other uses: 14%
Transportation schedule, weather updates etc...: 13%
Pricing and interface are too complicated: 8%

It'll be interesting to see the evolution of this data. In December 2003, AU introduced their NAVI-Walk service (personal navi service) with an aggressive TV campaign presenting the advantages of the GPS functions in a mobile phone (which most of their lineup had had for over 6 months already). Docomo knows that those ads work for them too; will they release all their new phones with a GPS? Will they come up with services that AU doesn't already have or will they pass this opportunity like Sony did with the LCD screens and fall behind this too (I haven't talked about Flat Rate packet download yet)?
Note that in the year 2003, and for the first time, AU subscribed more new customers than Docomo.