:set et sts=4 sw=4 ts=4
et = expandtab (spaces instead of tabs)
ts = tabstop (the number of spaces that a tab equates to)
sw = shiftwidth (the number of spaces to use when indenting
-- or de-indenting -- a line)
sts = softtabstop (the number of spaces to use when expanding tabs)
Also you might want to move 'colorscheme twilight' into the ~/.gvimrc file instead; it makes the .vimrc file cleaner when you separated out all of the gui-specific stuff.
My full vimrc and setup is here: http://github.com/bsandrow/vimc
{edit} Another good one:
By default Y is mapped to the equivalent of yy. This makes Y act like the 'copy/yank' equivalent of D. {/edit}