I just got home with a 70-200 IS rental (no manual to read) and noticed this lens has a Stabilizer Mode 1 and 2. What do these modes actually do?

mode 1 stabalize in both directions (side to side and up and down).

mode 2 stabalize in side to side only - used if you were panning on a tripod.

use mode 1 handheld.

Mode 2 is for panning, hand held or not. I use it often when I'm doing hand-held panning. It stabilizes in the direction that's perpendicular to your panning, so if you're sweeping the camera across the front of you (vertical shooting, or horizontal shooting), the IS will only stabilize up & down. It won't try to stabilize the side-to-side movement you're creating with the panning.

use Mode 1 for shots that aren't panning.

Thanks a million guys.