Sadly i'm at work, and therefore can't repeat the entire body of literature of utilitarianism, but in short -
Happiness here refers to peace, contentment and enjoyment of life (including the fulfillment of purpose), rather than purely physical or emotional pleasure. Perfect utilitarianism requires a perfectly weighted algorithm for calculating the maximum happiness generated from any action, which is largely impossible. An adequately weighted system attempts to provide everyone with a minimum global level of life enjoyment and focuses on the minimisation of unnecessary suffering (including but not limited to anguish, pain and grief), unnecessary here indicating suffering which does not yield a foreseeable net gain in happiness (and conversely, temporary happiness such as those described by SalmonGod or, less recently, Plato, that yield a net increase in suffering). In a perfect utilitarian system, not only would happiness be increased, but it would be maximised, so that, over the foreseeable future, each person's happiness would be maximised to avoid taking actions which, as an opportunity cost, deprive that person of yet greater joys.
Non-harmful desires, such as the desire to be free (personally this seems a tremendously foolish thing to hold as your highest ideal, but there we go) could be considered by a perfect utilitarian algorithm and indulged so long as it yields the greatest possible happiness for all affected individuals.
SalmonGod, your previous point, about going camping and experiencing difficulties are an example of suffering that yield greater net happiness. I go out and get myself thwacked at the weekends as often as possible. Sometimes it's muddy, too hot, exhausting and painful, but I do it because I experience total greater net happiness, both in the immediate because it's fun and I build emotional bonds with others, but also in the foreseeable long-term, because it's exercise and trains several skills which I take further pride in possessing. What you described in your meths post was hedonism, which is just short-sighted, egocentric (even nihilist) utilitarianism.
I should've been working. Post over.