Hi Jeff,
I'm glad you like it. It's my pleasure.
First things first:
JP> anyone using it would need to have an iPhone -- a concept that could trigger bar brawls.
If you get this you'll scare away anyone wanting to mess with your iPhone and avoid the brawls:
http://bit.ly/aC2XeG (iPhone 2G only)

JP>once a ride is entered by someone with the iPhone, the ride can be distributed to anyone who can make use of a gpx file. Am I getting that right?
Yes.
My general approach is that the rides themselves have to be freely shared. Garmin, Harley, Honda and others haven't seemed to understand that I don't choose my riding buddies based on their GPS or bike brand. This is largely why their ride-sharing initiatives haven't skyrocketed. I will charge for the tool to access the content (the mobile phone app) and for other add-ons that have value to riders - exact selection TBD.
JP>I guess the real value of the app itself is that iPhone users can comment on given rides (the same way yelp users can debate a given restaurant), which essentially uses "crowdsourcing" to keep information accurate and up to date.
Around cities where Yelp is prevalent I usually start talks with "It's kind of like Yelp for motorcycle roads." So yes.

That's exactly right. Over time, people will be able to keep others updated on the snow/road oil/police/downed tree/etc. status of their mutual favorites by adding comments and changing ratings. I'll also be building in weather and other features so it's useful on an ongoing basis.
JP>Okay, I live in China, a land of many great rural roads -- very few of which have been mapped for motorcycling. So, is China among those 35+ countries where Greatest Road users are happily mapping great rides? Or will I be the first??
Good news, bad news here. Bad we are not currently selling in China, mostly since I'd like to get the app localized into Chinese and be able to provide support in Chinese first. I looked through the map requests and there are maybe a handful of look-see's there, so you're practically the first. Good the app works in China since the Google Maps stuff we use under the hood knows the Chinese roads and can route between points.
Just to prove two points, I'll email you a gpx with a route from Yang Shuo to Guilin that I just entered. I'm sure it's not the most scenic choice (I don't know which roads give the best view of the towers), but it works in the app and in Google Earth. They're route points, which means it's up to your GPS to route based on your preferences at the time.
Thanks once again,
Daniel