  In this paper, we analyze and compare general development and individual
behavior on two non-profit internet-based hospitality exchange services --
bewelcome.org and warmshowers.org. We measure the effort needed to achieve a
real-life interaction, whereby the advantages of mutual altruism arise. The
effort needed is the communication quantified in units of time. Since the
amount of effort is not obvious to individual users, the development of the
effort investing strategy is investigated. The impact of individual behavior on
general development is discussed.
