Do bubbles in Guinness go down?

Why do the bubbles go down?

Up in center
Let's start at the point where you have just poured your pint of Guinness, and it is starting to settle.  At the inside surface of the glass, the bubbles are touching the walls of the glass and they experience drag - just in the same way as you can feel if you slide your finger along a glass surface.  At the center of the glass, the bubbles are not touching the walls, and are free to go up:  this is what bubbles of gas really want to do when they are in a liquid, as we are used to seeing. 
Moving out at top
The bubbles at the center rise rapidly until they get to the top, just below the head (the "froth").  In doing this, they have pushed and pulled the surrounding liquid with them. At the top, this liquid flowing upwards hits the surface and flows outwards towards the edges of the glass.
Bubbles go down at walls
The current is directed downwards by the edges of the glass.  As the flow moves downwards in waves, it pushes and pulls the bubbles that are hanging around at the edges of the glass. The flow can be seen as the dark lines of liquid (no bubbles) that wave quickly down the inside of the glass.
Cycle continues
What goes around comes around.  More bubbles flow up at the center, and the circulation continues.
Settled pint
Eventually the settling process comes to an end.  More and more bubbles have been deposited into the head of the beer during the settling, and the cycle loses momentum.
Circulating glass animation
In summary: bubbles at the center rise up and create a circulation in the glass.  The circulation causes bubbles at the edge of the glass to be pushed downwards.

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(c) 2004 Alexander & Zare