I use a Canon 70-200 f/4L non-IS, and I love it. It is one of canon's sharpest telephoto lenses, throughout its focal range. It's also really quiet. For someone who is looking into getting the best glass at a good price, I highly recommend this lens.
You can see samples on my photo site:
www.seatimepics.comMost of my boating/sailing shots were taken with the non-is 70-200. I've never used the IS version, so I can't compare. I do know there are guys out there at the boat festivals with huge expensive lenses that can't shoot. I just do the best I can with my non-is, and recommend it to those who don't have lots of extra money.