Vim used to have an edge when emacs was viewed as "bloated" for using 8 megs of ram, but now that's pretty negligible. On big projects I can get eclipse to use more than 2 gigs!
As a data point, my Emacs session is currently taking 75 mb RAM (on a 64-bit system). It's been up for a few weeks. That seems pretty typical.
While it's common to start and stop vi(m) frequently, Emacs is usually kept running, with shells, interpreters, etc. inside it. The start-up cost of loading lots of extensions amortizes over the total session. (And it just took about seven seconds for a new Emacs to start and load everything I use, FWIW.)
