What sort of thing is happiness?

In response to Donna McMillian's very instructive presentation to us on the topic of positive psychology or subjective well-being.  I was particularly struck by the persistence of this issue: we're not entirely sure what happiness is (though it might be a mood or some combination of emotion and cognition), nonetheless there seem to be measurable markers of its presence in our bodies and behaviors that are not only characteristic of those who are happy but also productive of that mood, emotion, or state of being.  Given these observations I begin to wonder if happiness isn't more an attitude or perspective than it is the result (or side-effect) of something else.  Is it the case that we are not so much made happy by what we have or by what we are doing as that we experience those possessions or activities from a happy perspective?  Of course some circumstances may promote or inhibit such a perspective, but can they really produce it?