There is a handy little bit of software that automates the process kon-tiki describes -- it's called MEAP
http://www.meap.biz/
it's been written by a user who was disgruntled that Steinberg flat out refuse to listen to their customers and add this feature to Cubase.
It takes a little setting up but, once working, it'll mean that you can go do something else while MEAP does the mixdown of all your individual tracks.
It's not expensive and gives you free upgrades for life...