Yeah I plow. I actually started plowing a few years before I started my lawn care business. I had a truck and plow for personal use and would plow a half dozen accounts on my way to and from my full time job. Some good points brought up about it. I do it mainly because I have lawn care customers who want it and I don't want them to hire someone else, who would likely be another landscaper. In fact I have picked up quite a few lawn care customers from plowing. But it is rough on me and on my truck and the income isn't reliable. One problem with it is that if you take on enough customers to bring in good money for the smaller storms it can be hard to get to them all in a timely manner for the bigger storms. I used to take any and ever account I could and my route just got too big area-wise and time-wise. It came with a lot of stress and sometimes resulted in me remaining out after me or my truck (or both) were no longer in any condition to still be plowing. I had an aging dedicated plow truck and made the decision to cut my route down to my core customers and a few others that were all very close to my home and cut all of my commercial accounts which required frequent service and exposed me to significant legal liabilities.
I have since sold that truck and put a plow on my newer truck. At that point I also changed how I billed. I used to bill "per push" with a push being defined as up to 6 inches. I now bill based on how much snow we get. I set a base rate for each account for up to 4 inches. 4 to 6 inches gets billed at 1.5 times the base rate, 6 to 8 gets billed at 2.0 times etc. So now I roll out as soon as we get 2 or 3 inches and can keep all of my accounts accessible at all times. They'll all close and for big storms I just open them up quickly and come back to do the detail work after the snow has stopped. Basically I increased both my pricing and the level of service I provide and that works out better for both me and my customers. I continue to be very selective taking on new accounts. I also close my list as soon as storm warnings are up. Everyone and their brother wants to be plowed when the big storms roll through. Not that I won't service some of them after my core customers are serviced (I have wifey keep a "call-back" list), but the accounts I want are the ones that leave it up to me when to plow and who want service even for the 2 inch storms.
One thing to consider is that plowing is essentially an emergency service with, as Kelly pointed out, a short window to get it all done in. You need to have a flexible schedule and be dedicated to doing what it takes to get it done and to get it done quickly and to be on-call from Thanksgiving to Easter 24/7. That's what it amounts to in my area anyway.