It was by pure luck (for me, as he has a car and can drive me to and fro the meetings) that I ended up in the same hotel as Peter for IIW2008a.
The lovely Ramada Inn Limited. Pool, hot tub and free breakfast. Business travel at its best.
It's the combination of Peter's bookings that is critical. If he and I were both in the same hotel but he had no car, then the benefit to me is limited, perhaps shared cab fare and some sarcastic and snide banter on the drive.
If on the other hand Peter had a rental car but was staying at a different hotel, then I would need to guilt him into picking me up and dropping me off each time. I've had great success with this ploy in the past but I don't like to overuse it.
What I would love is a hotel booking engine that, in addition to allowing me to filter hotels based on the normal criteria, e.g. free WiFi, pool, exercise room, etc, it would allow me to specify a search param of
"Only show me hotels where a friend who has rented a car are staying (and give higher weight to a convertible)"
This would be a special case of using your social network to help find services of interest and value, as in the diagram below (which I cant remember if I created, stole, or adapted)
In Liberty People Service, the rough flow would be
1) Expedia.ca, helping me book travel, discovers and queries my People Service to see my 'Travel Friends'
2) Expedia.ca uses info it gets from People Service to discover and query the 'travel calendar' of each of those friends
3) Expedia.ca uses info in my friends travel calendars to filter out hotels in my search
4) I ride for free