Why do curling stones curl?

Some theories out there:

• microscopic roughness of the stone by researchers at Uppsala University published in Wear: The asymmetrical friction mechanism that puts the curl in the curling stone
• liquid friction idea from Canadian physicist curlers
• The Straight Dope Scottish glaciologists diss Canadian physicists
• Australian journal of physics
• Curling research from 2000
• Assessment of the Sliding Motion of Curling Delivery in Elite and Subelite Curlers
• Nature Article: Study of curling mechanism by precision kinematic measurements of curling stone’s motion
• 41 page paper from 1998: Curling Scientific
• Science of sweeping