I handhold 99% of my photos and I use a macro lens constantly. Even if I had IS on my own macro lens I probably wouldn't use it because in my experience, all IS photos from a lens are a tiny bit softer than when the IS is turned off. It's subtle, I'll admit. The only reason I would use the IS is if I had to use available light.
I'm jealous of your camera though. It's the mark II right? I'm waiting for Nikon's equivalent, which will probably be 6 months or so from now I am guessing - Nikon aren't innovators in DSLRs but when they get around to catching up with the competition they build their DSLRs like tanks. I've been admiring the Canon 5D since the mark I came out.