Last night I watched an episode of Through the Wormhole discussing the possibility and feasibility of time travel. While the idea of time travel is interesting, I think the consequences of actually doing it might be dangerous, even disastrous. If your travel into the past or the future were interactive, you probably could not avoid altering events that might change the present. Even if it were not interactive and you were only an unseen observer, your knowledge of past or future events would alter your knowledge and perceptions in your present, potentially changing your time line.
We need to live in the present moment. Having the ability to go back in time to change the past would have unforeseen consequences in the present and in the future. Knowledge of future events would affect our actions in the present, thus altering the future. It gets quite messy rather quickly. It could also affect past, present, and future events in parallel universes. Screwing around with the space-time continuum is not something to be left to amateurs and we are all amateurs.