Traveling to the past could take place from a limited free-will view, perhaps, that way it would be as though you weren't truly there, but only watching it. But that would stink. No character interaction, something I'd really want. Traveling to the future...if I do that in what I'm working on (assuming I stick with it!), the time traveler will most likely not remember the whole thing, since it really didn't happen, and that way he wouldn't be able to make great predictions in time and so on.