I like having perldoc output to a split window, and I wanted to output module documentation if you were on a 'use Module;' line, so I recently came up with this (my vim-foo could probably be better):

function! PerlDoc()
  normal yy
  let l:this = @
  if match(l:this, '^ *\(use\|require\) ') >= 0
    exe ':new'
    exe ':resize'
    let l:this = substitute(l:this, '^ *\(use\|require\) *', "", "")
    let l:this = substitute(l:this, ";.*", "", "")
    let l:this = substitute(l:this, " .*", "", "")
    exe ':0r!perldoc -t ' . l:this
    exe ':0'
    return
  endif
  normal yiw
  exe ':new'
  exe ':resize'
  exe ':0r!perldoc -t -f ' . @
  exe ':0'
endfunction

"Display docs for built-in functions when cursor is on function name
"or for modules when cursor is on 'use' or 'require' line.
map ,h :call PerlDoc()<CR>:set nomod<CR>:set filetype=man<CR>:echo "pe
+rldoc"<CR>
[download]

Updated. (I knew nothing about Vim programming before I started this...it took a couple of hours to come up with the first version of this, so comments, etc., welcome).
Update: Added set nomod.
Update: Added filetype, C-M=>CR, echo message
Update: added -t