A mobile and ubiquitous computing motivating example: the business plan is
helping people with shopping.
The whole scenario is somewhat complicated, but can be simplified arbitrarily, to fit our purpose.

0- We specify what we need to buy on our PDA or portable computer (price range, brand names, maybe specific stores, etc.).

1- Data on parking space availability (full/empty) can easily be gathered with current parking meters, or a minor variation of the current ones, i.e. compatible with current technology.

2- Car location is specified with GPS.

3- We are prompted for where to park the car, and which store to go to.

4- When we need several products, constraints like minimum price (for grad student shoppers), minimum distance (for elderly shoppers), etc. can be optimized depending on user needs.

5- We can determine if we would like unsolicited ads or not (as we are passing by in the street), the distance from which we would like to receive ads could be specified (defaults).

6- Our location can be determined using GPS, cell phone, PDA, internet connection, etc.

7- Privacy could be preserved, since unique people are not necessarily identified. The other option is to trust that our data is in good hands.

8- Enabling technology is very close. Right now, the San Jose area is creating wireless access for the whole city area for free. I wish I had a house there!

9- Having wireless access, all this can be deployed on top of the web technology. No need to reinvent the wheel!

10- People would be more than happy to pay for such a service, considering: 1) the time saved, 2) gas prices and not driving around for no reason, 3) possible discounts from stores, and 4) more convenient shopping based on the user constraints.

11- Shops are more than happy to pay for such a service to attract customers. As soon as it is implemented, we can bet all big names would jump in to advertise.

12- We are happy that we can make money, theoretically, as long as one of the above two steps are realized. Actually, doing a cool project comes first!

It looks more attractive than habitat monitoring and measuring temperature and humidity with sensors. The whole project seems to have good financial incentives.