What is the difference between dragging a folder over to the Ubuntu One folder for syncing and just checking the "synchronize this folder" check box on each folder I want to sync?
The "Ubuntu One" is the default folder, that is always synced when you enable Ubuntu One. For other synced folders, you can select in each devices which to sync or not sync.
- on PC "A" you have "Ubuntu One" folder, and Pictures folder; you select "Pictures" for syncing.
- on PC "B" you also enable Ubuntu One service: the "Ubuntu One" folder will be synced, but you can avoid to select also "Pictures" syncing.