Yes I've heard issues of the IS on 70-200 2.8L IS....you have to take extra care to check if buying 2nd hand. I had a friend who recently bought a 300mm f4L IS 2ns hand, there was some problems with the IS...made some loud noises and such.
Normally to minimize handshake the universal rule of minimum shutter speed of 1/focal length is applied. So at 200mm, comfortable shutter speed for handholding should be above 1/200 (say abt 1/250). For me, I mainly use the 70-200 indoors and most of the time on monopod, so I did not go for the IS feature. You can also pump up ISO to keep your shutter speeds up. (of course more noisy lar)
For outdoors in daytime, normally shutter speeds of above 1/200 are easily attainable, so no worries for handholding there. Unless your hands are really shaky.
How bad is the shake really? Not that bad lar...just needs some practice and techniques when handholding...after some time you'll get the hand of it. Just that you're liable to get tired after some time handholding the lens, thats when the IS comes in useful.