Heck, I've gotten some sharp shots with it at 1/30 (below)... Tho they were mixed in with a fairly high percentage of shake blurred ones. Of course, I usually try to use it at more reasonable speeds... But what the heck, I'll try almost anything. The Sun Worshipper.EF 135mm f2L lens at f5.6. EOS 7D camera at ISO 400, 1/30 shutter speed. Handheld, ambient light (+1 EC).
Seriously, on a full frame camera, you should be able to hand hold at around 1/125. On a cropper, you'd likely want to bump that up to 1/200 or faster. Maybe you can manage a little slower with a good keeper rate, maybe you'll need a little faster... The old "shutter speed reciprocal of the focal length rule" is really just a general guideline (full frame... multiply by 1.6X for crop)... We're all different and might get better with practice.
It's a gorgeous lens that I love to use on full frame in particular. I ordered mine the same time I got my 5DII (my return to full frame after 5 years shooting with nothing but croppers).
But I really like it on either format... 7D, handheld at 1/30: