There is a good description of the daguerreotype process on the Library of Congress site.
http://memory.loc.gov/ammem/daghtml/dagdag.html
Two things really strike me when I read this:
a. you had to hold the plate over hot mercury to develop it. Yikes. Talk about the mad hatter. It must have been the mad photographer.
b. the exposures were 3 to 15 minutes! Pretty hard to get anyone to stay perfectly still for that long.
