- No. It's entire purpose in life is to be a usb host. The arduino is already a usb client, so you wouldn't need a shield for that. The arduino generally acts as a virtual serial port, but newer arduinos that use the Atmega8U2/Atmega16U2 as a usb/serial converter can have that chip reprogrammed to act as different usb devices.
- You could attach an android based phone/tablet to it, download the android open accessory development kit from google and write a quick android app that would see the data. I believe that there are usb loopback devices that can be attached, that simply send back whatever they receive. Don't forget that most usb devices, other than HIDs like keyboards and mice, will require you to write the equivalent of a driver to communicate with them.