What's in your .vimrc file?
aristoxenus: Some I like:  " Keep cycled-away buffers open (preserving undo, 
  " allowing buffer switch without write)
  set hidden

  " Facilities for handling pasting into vim, preserving
  " indentation of the pasted text.
  " This will make <F4> start paste mode and <F5> stop paste mode.
  " Note that typing <F5> in paste mode inserts <F5>, since in paste
  " mode everything is inserted literally, except the 'pastetoggle' key
  " sequence.
  map <F4> :set paste<CR>
  map <F5> :set nopaste<CR>
  imap <F4> <C-O>:set paste<CR>
  imap <F5> <nop>
  set pastetoggle=<F11>

  " Toggle line-numbers with key sequence Ctrl-N-N:
  nmap <C-N><C-N> :set invnumber <CR>

  " Consolidate swapfiles to keep working directories clean
  set directory=~/.vim/swap