Raspberry PI and Arduino as a portable platform for usb devices?

Question

Arduino

Raspberry PI and Arduino have a usb connector, can it be used to connect some usb device to Raspberry PI and Arduino, read data from them and operate on them?

Answer 1

Raspberry Pi is a complete USB host. Everything that has drivers in the OS will work. Well, what is enough power - it is difficult to pump enough current through thin raspberry tracks for, for example, an external HDD without additional power.
Arduino - check the documentation for the specific board. Usually only the client, but maybe modern ones are already stuffed and the host implements it themselves.

Answer 2

Yes, there is a USB Host Shield for Arduino, as well as an Arduino ADK version. You can connect to them, for example, a mouse, keyboard or even an Android phone.