trust, trustworthiness and responsibility

Last night at the Work Foundation / iSociety event on Social Capital and Social Software, link to report (pdf), the concept of trust was discussed as an important measure of social capital. David Halpern clarified this saying that is trustworthiness which is being measured.
The response to the question 'can you trust people' shows overall decreasing amounts of trust in most places in the world. The Nordic countries are generally high and rising, the southern European countries are lower and static, The Anglo-Saxon countries (Australia, New Zealand Ireland, UK & USA) are all falling. The Latin American countries are the lowest, with Brazil measuring 3% last time. The UK is on around 44 and the Nordic countries around 60.
There is a distinction between formal and informal measures of trust, with informal measures, usually person to person, rising. Whereas the formal church or institution trust levels are falling.
Trust is a decision between two agents, trustworthiness is the overall measure of how people many of these decisions are positive. I think that this misses out on an important concept, that of responsibility. When you allow people to leave comments on your website you trust that people have enough responsibility not to leave abusive comments on your site, The same is true when you put flower pots outside your house.
When you have to make the decision to trust someone you must use some metrics to assess this. The assessment will also be context dependent, I'd trust someone to buy me a drink in return, before I'd trust them to deposit cash at the bank or look after a child. This assessment is based on several levels. There is your own level of social responsibility through which you can guage others. There is also your impression of the other agent, which is partly their reputation and partly your assessment how responsible you think they are. This is based on context, we usually trust the police, due to the responsibility vested in the uniform.
An example, I was recently in Italy visting Venice and several times people tried to short change me. This happened in Milan airport duty free shop and in a couple of bars. Each time I was a one off visitor and thus there was no trust between the shopkeeper and myself. When I challenged there was an immediate backdown, like they were just trying it on. I was most surprised in the duty free shop, as I assumed, wrongly, that the more formal setting made it less likely, whereas in a bar I checked my change each time. It is possible that the lack of trust due to the frequency of short term interactions, seems to diminish the responsibility of the shop keeper. The short term interactions also provide a context in which the chance of getting caught is low, as people are unlikely to return to the place. The duty free shop was the only place where they were successful.
If we miss responsibility out of this analysis then there is no space for individual action. Why does someone correct a comment on a blog, or hold a door open for someone, it is not from trust. It is because the person feels that is is appropriate to act in a socially responsible manner.
Responsibility is owned by the person who forms a trust with another person, if there are many of these trusting actions, then a general feeling of trustworthiness will evolve.