I recently watched "Hot Tub Time Machine," which was plenty funny even while using a silly concept. It was cute, had some good dry humor, through some bare boobs in to draw the 15 year olds and so was probably not the worst movie I've ever seen. For me it reminded me of how much I hate time travel as a plot point. It is one thing if you are trying to use time travel to make some sort of philosophical point. I like Christmas Carol, and Connecticut Yankee in King Arthur's Court, both which bend the rules of time, but when you use it to correct only to get the writer out of a corner he backed his self into, it is really annoying. Star Trek did it with their recent movie and it pissed me off. In Star Trek 4 they went back in time, but it was to correct a problem in the future. They went back and then forward again, and didn't travel around randomly changing the plot and course of the story as they went as well as the characters who are affected every time a change is made. It just seems lazy to me. It doesn't allow the reader to predict what might happen and not in a good way. Readers like to anticipate the next page, and like to be fooled, but also like to believe that the plot is possible. With time travel all of that is removed. You can't predict what might happen because rime travel is not based in normal human understanding. Even for the science fiction reader the plot and characters can get too complicated to follow. So I vow to never use time travel as a literary tool. Except that I have a story that features it a bit…ok, I guess you can use it, but don't expect me to like it. And "Hot Tub Time Machine" was still funny even if the idea of traveling time in a hot tub with drunken naked men is dumb.