Not sure the point about a gentle breeze - if it's moving the subject then no IS in the world is going to help. If the tripod is unstable - say a heavy wind, then there's no problem leaving it on regardless of the design, the point is that the drift is very noticable - if you see it drift, turn it off.
Well, the other day I was shooting some landscapes with my Canon 70-200 IS. There was a gentle breeze blowing, with occasional soft gusts, probably no more than 10 mph.
I have always left the IS off when using my tripod, a Manfrotto 3001, I think is the model. I use a remote trigger, and I will often put my hand on the tripod after the mirror lock up to steady the tripod if there is any wind.
Especially with that lens, my heaviest, I thought I could feel a vibration in the tripod from the wind, and I was glad to have my hand on there. I was just wondering, after reading this thread, if the IS system would be useful for such small excursion, high frequency movements such as might be produced by wind.
The IS system, as I understand it, uses gyros. Once they spin up, we are dealing with the physics of perturbing their effect. I have no idea how the equations for such a process would look - I leave it to the physics Majors to explain if the effect is linear or exponential, tiny or strong at small values, etc.
I am selling this lens, so any discussion is academic for me, but I thought it was a somewhat interesting question, which might shed a little light, that's all.