suppose you could set the file pointer using seek

One thing to watch out for -- the DATA filehandle is open to the original source file, so if you seek back to the beginning, you'll need to scan forward to the __DATA__ marker again to read the contents a second time.

You can use this to turn your script into a quine, that is, to enable it to print its own source code:

  seek DATA, 0, 0; 
  print <DATA>
  __DATA__
[download]

(I recently found this trick in the TinyWiki source code...)