We had that same problem here in St. Louis in the beginning of December '06. I think we ended up with 3-4" of ice on the ground. I had nothing in my contracts on how to deal with sleet and freezing rain so I spent about 4 times as long to clean it up than what snow would have taken (for the same price).
Does anyone have lines in the contract about ice on the ground as opposed to snow?
We have a statement about Ice starting at about 1/10 of an inch and sleet. It is all based on the idea of salt and clear. We are VERY upfront with our customers about what we will do and what to expect. However in bad Ice storms (we very seldom get) we will always let the property managers know it is going to be a BILL$$$$$$ It always helps when they know it is coming.
For this storm I'm going to charge my normal rate for 1"-4" of snow, we'll say around $45 per house. For that I will include a light salt sprinkling on steps/walks or charge 5$-10$ for salt if needed since I use none or little usually. This time though (we had 3-4" of hellish ice/sleet/rain/snow) I', going to charge the $45 plus $25-$35 for salt. I used at least a full 50 lb bag at each house. So total will be around $70 per house.
I don't have anything written in my contracts, but I definately am going to think something up for them next year, because you guys are right, it is a lot more work to move sleet than it is to push that nice fluffy snow.