So I'm watching Deathly Hallows 1 today. I know the book and movie differ, but I don't think they differ regarding this. Snape hides the sword of Gryffindor's in the lake and sends his doe patronus to Haary to follow to the sword. While Snape could just have his patronus "find Harry and lead him to the sword," wherever he happened to be (a point I'm not sure of either), the sword was relatively near to where Harry was. In the movie (at least) the doe also led Ron back to Harry. Again, I suppose we are to assume Snape could tell his patronus to "find Ron and lead him to the sword"--that Snape did not take the chance that Harry and Ron were together. While Ron thought he was being led to Harry, he was actually being led to the sword, and Harry happened to also be there. Ron does say he followed the doe for a while--unsure how long--but he was led at least a distance while Harry was damn close to sword. Did Snape know where Harry was when he hid the sword that he was able to hide it so close? Otherwise, Harry could been running over hill and dale to find the thing, kinda like Ron did.