The path to success lies in finding something stationary to shoot. Don't worry about having people walking through your shots; they won't trip Photosynth up, so long as you have decent coverage of the building, tree, or whatever you're synthing.
When I warn off of shooting moving objects above, I'm only saying that if you give Photosynth 200 photos of your family walking through a park and expect a 3D model of your family, that is not what you're going to get. If you took all of those photos in one part of the park and your shots are evenly spread out enough and overlap each other, then hopefully you'll get a model of that bit of the park, but not too much of the moving stuff is going to make the cut.
For more info, see the Photography Guide and brief Video Tutorial here:
If you have more questions, feel free to come back and ask more.