i use mac os 10.7.3 and the latest stable MacVim snapshot. I use two monitors, so on the first, I have MacVim in the non-lion-fullscreen mode, and on the second i have skim open, to see my output.
for simplicity, let's assume, that MacVim in full-screen mode hast 30 lines and 100 colums. I like to have my texted centered, when i work on it, so i set to
set lines=27 columns=85
a funny thing happens, every time the monitor setting is changed, i.e. when i disconnect the second monitor, or when i close the laptop to only use the external monitor. the setting automatically goes back to 30 lines and 100 columns.
something related: when i used
set fullscreen guifont=Menlo:h25 columns=80 lines=26
the last setting (lines=26) is not executed.