It does work for cumulus, as they are formed directly by rising air. Theres bucket loads of stuff on lapse rates and such, and as a glider pilot I would love to tell you all about it. Unfortunately it fell out the back of my head last October as the soaring season finished.....
Try looking at
http://www.itadvice.co.uk/weatherjack/wx-FAQs.html
and
http://www.itadvice.co.uk/weatherjack/STARS.htm
which has a tutorial on soundings on a link at the bottom of the page.
Cheers
John