One of the biggest problems with Crosstrainers, is that new users will often find that they will develop sore calf muscles. This is simply due to having the heel position on the crosstrainers foot plate, namely the heel is extended upwards throughout the exercise. You should aim to place your heel down on the foot plate when ever you can, in order to stretch the calf muscles.
The crosstrainer is a great piece of gym equipment for those that require a gentle workout, or who suffer from lower leg injuries.
If you go into any modern gym nowadays, you will often see rows upon rows of these machines, all for the same reason - gym goers love them - if you ask the regular gym goer what they find hard to use, then you will often see this piece of gym equipment unoccupied.
Because you're working both your arms and legs, the calorie expenditure for these machines is claimed to be similar to that of running and rowing, however this is simply not the case - momentum is doing a lot of the work, and if you rest your arms your hardly notice any change in either speed or exercise difficulty.
Cross trainers are designed to keep the regular gym goer, at the gym, with the under standing that they are actually having a good workout.
This is partly true, because they are actually working out, with very little stress placed on their muscles / joints, which will result in no or very little muscle soreness, however for greater benefits in a shorter time, exercises such as running - rowing - cycling should be considered for those who are physically capable.