I just installed Ubuntu One files for Android and it uploaded all my pictures and I can see them in the web interface. Can I get this folder to automatically download all the files to my Ubuntu One folder on my Ubuntu PC?
Yes. Your pictures are stored in a cloud folder named "Pictures - your phone model". If you run the Ubuntu One control panel (which you can see at https://wiki.ubuntu.com/UbuntuOne/Tutorials/ControlPanel#Cloud_Folders) then your new cloud folder will be listed, and you can tick it to make sure that this cloud folder is also on your computer.
You should see a new cloud folder called something like "Pictures - Nexus One", which you can specify in the Ubuntu One control panel to sync to your computer. It doesn't sync down by default, no.