I made a little vimscript to automatically cd to the project root of a symfony project. It makes it easier for me to use the ctags :-)

"-------------------------------------------------------------------------------
"  Description: Finds and cd to the symfony root of the project
"    Copyright: Copyright (C) 2009 Geoffrey Bachelet
"   Maintainer: Geoffrey Bachelet
"      Version: 1.0
"-------------------------------------------------------------------------------

if exists('find_symfony_root_loaded')
  finish
endif

let find_symfony_root_loaded = 1

if ! exists('find_symfony_root_symfony_executable')
  let find_symfony_root_symfony_executable = 'symfony'
endif

" root detection when opening a new vim seems to work
" only if these two events are bound. not sure why.
autocmd BufWinEnter,BufRead * call FindSymfonyRoot()

function FindSymfonyRoot()
  let l:cwd = GetAbsoluteDirname(@%)
  let l:symfony_root = findfile(g:find_symfony_root_symfony_executable, l:cwd.';')
  let l:symfony_root = GetAbsoluteDirname(l:symfony_root)
  if strlen(l:symfony_root) != 0
    execute 'cd '.l:symfony_root
  endif
endfunction

function GetAbsoluteDirname(path)
  let l:path = a:path
  " gets the dirname
  if !isdirectory(l:path)
    let l:path = strpart(l:path, 0, strridx(l:path, '/'))
  endif

  " makes it absolute
  if match(l:path, '/') != 0
    let l:path = getcwd().'/'.l:path
  endif

  return l:path
endfunction

note for later: add vimscript support to geshi

Or see the highlighted version on gist.