On balance, I hope to be a realist. Things are what they are, some good, some bad; one woman's sorrow is another woman's blessing; one man's loss is another's gain.
One thing I have noticed about professional optimism advocates: they tend to be predominantly white, well off, and the offspring of prosperous parents. Edit in: and male.
How much is nature? How much is nurture? Is it easier to be optimistic when one is born to privilege?
How do we differentiate optimism, per se, from desperation, or from whistling in the dark?
Conversely - how much of pessimism is, like exogenous depression, a reasonable response to unreasonable circumstances?
Barbara Ehrenreich's latest book, Bait and Switch, includes a wonderful discussion of the blame-the-victim mentality and 'magical thinking' - both mislabeled as optimism by their practitioners - that she encountered while studying white collar unemployment, support groups for downsized employees, career counselors and so forth. It's an extremely absorbing book, well written and brilliantly perceptive, and an excellent counterpart to Nickle and Dimed, her book about trying to live by doing minimum wage work.
That being said - there's no substitute for genuine optimism, for faith, for hope, and for the commitment to growth that gives faith and hope their traction in the human heart.