I've recently discovered the fun of using watercolours for this, adding the thrill to this already little odd situation (someone you don't know standing naked before you for arts' sake) that you can't correct or erase. I've found it to be good practice and education -- this way you have to draw correctly from scratch. Indigo, used for the quick poses, is particularly difficult to wash out, delightfully smudgy, very easy to do shadings with...
The most difficult thing -- as I'm no regular croquiseur -- is to think of the body merely as a body -- one attempt failed miserably as Beauty and Artist momentarily got accidental eye contact; quite distracting...
