kokopedal: a "quid" is a slang term for a Pound Sterling - similar to using the term "buck" for a dollar.
b00sk: Basically, anything you would do comfortably with a pen and paper - such as drawing curves, handwriting or precise colouring - will benefit from a graphics tablet in Photoshop (or similar applications). As to which to get - well, that depends very much on your budget. Wacom are the industry standard, but are also pretty expensive. Personally, I use a Trust TB-2100, which works fine for me:
Amazon.co.uk: TRUST TB-2100 WIRELESS TABLET: Electronics & Photo: Trust
Amazon.co.uk: Wacom Bamboo One Graphics Tablet: Electronics & Photo