Based on the single fact that in ancient times the world was believed to be infact flat, it becomes much more likley that a flood could have happened over perhaps just a country or large area (because extensive travel was not possible). The perception of our ancestors that the world was in fact a small place as compared to that of today will justify their description of a flood that engulfed the world.
It 'is' impossible to build a boat of that size, to hold all animals on earth. Also the fact that many animals can not be found in such places is further evidence against it BUT, like many of you have already said, if this man was protecting his herd and many other animals around the area, it will suddenly appear feesable that he has protected the animals in his surrounding area.
I was watching a show on this yesterday; on fox. Their are many people who still are activly involved in the search for Noah's Ark. Many of who (a very large percentage) believe that the ark can be found on the peak of Mount Ararat in Turkey. Now broken in two, the ark is apparently buried beneath the glacier atop the mountain. CIA satelite photographs indicate that a boat like vessel is atop the mountain but the further investigation of the mountain has seen the photos become classified and not available to the public.
Many people who travelled to the top of the peak to find it have not recovered any more evidence other than pieces of timber which have been sculpted by hand. These timbers are found to be oak or a vintage around 3000 years old (not old enough for noahs ark as the story is told) but the timber isn't available or grown anywhere around the area for a couple of hundred killometres. The fact that Oak timber, found at the top of a mountain, hundreds of kilometres from where it should be found, in the form of a boat like vessel gives strong evidence to the Noahs story or a story of a flood and a man using the boat to save himself and his flock or native animals. Then again a flood that reaches 1600 feet in height is also improbable but a wave that travels 3km inland would have had me saying "no" before boxing day.
Its very interesting indeed.