Drupal 7 takes more memory per server thread than Drupal 6,
reducing the number of threads that can be run on a given server, and
raising the minimum requirements for a VPS. This impacts not only
bottom-scraping hosting, but also "real" infrastructures, where
process size is sometimes viewed as a necessary evil solved by buying
RAM.

I will offer comparisons of D6 versus D7 memory usage in various
configurations and a few simple attempts to reduce it. I have no magic
bullet solutions; my main goal is to get good ideas from the audience,
and perhaps cause process size to be given more consideration in
future development.