This article is from the Running FAQ, by Ozzie Gontang with numerous contributions by others.
The lack of wind is definitely a problem, and as mentioned above a fan
is a necessity. Another problem with treadmills is boredom. I am always
amazed at how much faster an hour passes when running outside than when
running inside. I don't think you can expect to read while running on a
treadmill, but you can watch television or listen to music. I generally
prefer loud music over television, but this is obviously a matter of
Another thing to be aware of is the tendency to set the treadmill at a
fixed speed and incline and run an entire workout at these settings. I
would recommend varying both speed and incline to give your muscles some
variety and minimize the possibility of injury.
Some treadmills interfere with heart rate monitors and prevent their
use, though there are treadmills which come with built-in heart rate
Safety is of some concern, and many treadmills come with protective
devices which stop the belt in case you slip or fall off. Treadmill
manufacturers always recommend plenty of clearance between the treadmill
and the walls of a room. Treadmills can draw a lot of electrical current,
and 30-amp circuits are recommended for some heavy duty models.