If you could link this idea up with a social network you may be able to increase the trust level by searching within your social network, perhaps by extending that network by one or two degrees of separation. If everyone that you know and all of their friends entered their vacation plans into a database so that you could find someone that you have a chance of trusting who could deliver your package, you may be able to make it work. On the other hand, now people have a way of finding out who's going to be on vacation and when, that could be bad.