Regarding video synthing, the Photosynth team has admitted that they have experimented with it, even before releasing Photosynth in August of 2008, but nothing has been released yet.
For now, it is pretty simple to use something like VirtualDub or Quicktime Pro (depending on the format of your video) to convert your video to an image sequence in one simple step. Putting every image or a subset (such as every other or every tenth frame) into Photosynth can be easily accomplished by viewing the folder as thumbnails, allowing the file selector to be wide enough to fit the appropriate number of photos in each row and then select one of those columns to put in the synther. (e.g. two columns for every other photo; ten columns if you wanted to select every tenth frame)
Downloading the pointcloud is fairly simple nowadays due to some Photosynth users' hard work. Download their tool here: http://pspcexporter.codeplex.com/