A wired mouse will connect via the USB ports in the Model S but (in my experience) a wireless one will not.
A thumb drive will connect.
A wired USB keyboard but not (in my experience) a wireless one.
What have you tested?
I had a USB Logitech Track Ball laying around and decided to plug it in. A blue dot appears when you move the track ball. It goes away once you stop moving the trackball. You can select an item by pressing the track ball left button.
I have a USB hard drive formatted with the Linux EXT4 filesystem. It works great for my FLAC music collection. I also have a bluetooth keyboard with a bluetooth to USB adapter. No luck there with either the adapter or bluetooth. I also tried a USB DVD ROM drive. Again, no luck.