I ran steamers this Winter to remove ice dams and it worked quite well. Started the year with one and now have three.
Minumal fee for shoveling and steaming, 2 hour minumal $500-750 (depending on height, pitch, and yes, demand).
Low pitch roofs we harness off and steam from the roof. High pitch roofs we steam off the ladder which is a really wet ordeal.
We used low pressure steamers from Northern and when 0 degrees or better they worked great. When below zero however they seemed problematic. The trick was to set the pressure as low as possible while still having 250 degrees water.
As far as productivity the warmer the day the faster the ice dams came off. On the coldest day the slowest was on a 18in ice dam which went back about 5 feet, 8-9ft per hour. On the warmest day the fastest was a 8in ice dam that went 3 feet back, 70ft in about an hour.
Most ice dam removal averaged around a grand but one we did was $2,700 single family.
The leads came in word of mouth, phone book (2+ years old), Angies List, and Google.
Two Monday and Tuesdays back to back weeks got about 30 calls per day.