I have shot a lot of macro.
I almost never use autofocus, (no choice with MPE65) but not with Sigma 180 either. I never use a tripod. (other than a small tabletop with a beanbag placed on top, don't actually attach to the tripod)
I have tried extension tubes with 24-105 and 300 F4 IS and in both cases I found IS useless.
I'm not unique in my technique. With an MP-E 65 the only option would be a tripod anyway.
MP-E 65 technique is attempt to locate subject in the viewfinder, not always possible. Once located it's a matter of composing then trying to stay motionless at the distance focus is achieved. Usually I try to time my shots as I rock back and forth, watching the subject coming into focus then blurring again. (DOF will be typically fractions of a mm, it's not like I can't keep still)
With Sigma 180 I manually set focus at MFD and then use same techique as MP-E65. (when shooting macro)
So the problem with IS is it tries to compensate for my movements. Back and forth it makes no difference, but up and down it compensates. (rare my body movement would be perfectly perpendicular to plane of focus) Pretty soon it runs out of available adjustment and resets causing the whole scene to jump in the viewfinder.
At lower magnifications I could see the use of IS, but for anything close to 1:1 or more, IS is no help to me.