I recently cut out a good size window in an evercase and went through 3 cut off wheels. People just get too impatient and wreck the wheels while cutting.
Ya, my first thoughts were that I was being too rough with the wheels, but trying to be more gentle didn't lead to any improvement in the life of the wheels. It took me 6 wheels to cut a huge window in my full tower, and another 14 wheels to cut a design and some text into the right side panel. Nothing was too complicated, but as soon as the wheels start to grab in the metal, they seem to disappear quickly. It's definately possible that I just don't have the patience, but I was really trying to keep the number of wheels down for the right panel, and I didn't do that great a job, although the panel looks great.
On a related note... are the non-reinforced cutting wheels of any use? I notice they are quite a bit cheaper, and apparently will cut metal if you buy the right ones. All of the non-reinforced cutting wheels that came in my kit when I bought it were broke, so basically I got a bag full of little wheel chunks.