Just got a new pocket camera (a Canon SX230HS) to replace that one, read the manual (I can’t help it), and discovered that they recommend turning image stabilization off for tripod shots. A bit of rummaging turns up conflicting advice, so I figured a quick test was in order.
[Edit: it's really the Canon SX230HS, not the 320 as I originally mistyped. I'm not changing the post's permalink, for obvious reasons, and I'm stuck with bogus filenames. Grumble, etc.]
This is a dot-for-dot crop from two images of the torso of the Pink Panther Woman in black ABS, showing the rather nasty seam produced with Clip = 0.1. The pix are seconds apart at f/8 with manual focus and flash illumination, so they’re as alike as I can make them. Clicky for more dots.
Pop quiz: which side has stabilization turned on?
Answer: left = ON, right = OFF. Yeah, I was surprised, too; even the dust specks look the same.
So, as nearly as I can tell, image stabilization doesn’t add any jitter to a tripod shot. At least not on the scale I’m using, which is a Good Thing: turning it on & off requires a trip through the menus.