I know that Han-Wen fixed a huge number of memory leaks sometime around
version 2.11.12; I think a few have crept back in. I was just compiling
the docs, and lilypond's memory footprint went above 300 megs (I stopped
it then and restarted it). I have no definite numbers, but I'm pretty
certain that lilypond didn't use that much memory when I was compiling
the docs a few weeks ago (with 2.11.18).