(NOTE: There's a more up to date version of this in the General C++ Settings section.)

Finally! Vim's decision to add a 'shiftwidth' to everything I type when I'm inside a namespace is thoroughly annoying and there appears to be no "standard" way to fix this in Vim aside from writing your own function for use in the 'indentexpr' option.

Well I finally got around to writing this up and, while extremely crude, it appears to work alright. You'll find the function definition below as well as in the General C++ Settings section.

" Fix up indent issues - I can't stand wasting an indent because
" I'm in a namespace.  If you don't like this then just comment
" this line out.
setlocal indentexpr=GetCppIndentNoNamespace(v:lnum)

"
" GetCppIndentNoNamespace()
"
" This little function calculates the indent level for C++ and
" treats the namespace differently than usual - we ignore it.  The
" indent level is the for a given line is the same as it would
" be were the namespace not event there.
"
" This function is rather crude but it works.
"
function! GetCppIndentNoNamespace(lnum)
  let nsLineNum = search('^\s*\\s\+\S\+', 'bnW')
  if nsLineNum == 0
    return cindent(a:lnum)
  else
    let incomment = 0
    for n in range(nsLineNum + 1, a:lnum - 1)
      let cline = getline(n)
      if cline =~ '^\s*/\*'
        let incomment = 1
      elseif cline =~ '^.*\*/'
        let incomment = 0
      elseif incomment == 0
        if cline =~ '^\s*\S\+'
          return cindent(a:lnum)
        endif
      endif
    endfor
    return cindent(nsLineNum)
  endif
endfunction