I have got a GP-1 on order from Nikon and will start using it straight away. I had a look at a few different ones, but the Nikon (overpriced?) looks like the least hassle to use. A couple that I saw, registered up to 1000 pics in the logger, then you have to download the data to the computer and load the data to the pictures at a later date - looks like far too much hassle, the GP-1 tags it straight away.
Basically it is a reaction to numerous customer's requests going back years. "Which corner was that taken at?" Is the most common question. (baring in mind I shoot at race circuits) So in future the customer can find out for themselves if they really want to.