Validate Upload Script

I'll be allowing users to upload certain files on my website and have put together the below script.

Can anyone see any problems with it? Any suggested improvements?

<?php

      $FileUploadSuccess = 0;

      $uploaddir = 'files/';
      $uploadfile = $uploaddir . $_FILES['img1']['name'];

      $filetypes = array("image/jpg","image/gif","image/jpeg","image/pjpeg");
      $imageinfo = getimagesize($_FILES['img1']['tmp_name']);

      //check file size is less than 2MB (below is bytes)
      if ($_FILES['img1']['size'] <=  2097152)
      {
            // upload the file only if the file type is of one listed above.
            if(in_array(strtolower($_FILES['img1']['type']),$filetypes))
            {
                  // rename the file.
                  $path_parts = pathinfo($uploadfile);
                  $uploadfile = $uploaddir.(substr($_FILES['img1']['name'],0,(strlen($_FILES['img1']['name'])-(strlen($path_parts['extension'])+1))).date("YmdHis").".".$path_parts['extension']);

                  if (move_uploaded_file($_FILES['img1']['tmp_name'], $uploadfile))
                  {
                        $FileUploadSuccess = 1;
                  }
            }
      }

      if ($FileUploadSuccess == 0)
      {
            echo "File Upload Failed for some reason - display error message with likely reasons";
      }
      else
      {
            echo "File Upload Successful - display happy message";
      }

?>