I just got the 24-105 last week and so far it's been very nice. I use it on a tripod when I'm doing portraits and such and I'm wondering about the IS. In my 300 f2.8's instructions it specifically says to shut off the IS when using that lens on a tripod. But the 24-105's instructions are more vague. It mentions shutting the IS off to conserve battery power in the camera, but it doesn't suggest that IS will actually hurt image stabilization when using a tripod; as the 300's instructions clearly state.
The 24-105 is using a newer type of IS than the 300's, so things are likely to have changed. In any case I'd like to know what kind of real-world results other 24-105 users have experienced with IS and a tripod.