For those of you who wondered, as I did, here's what perl -lpe '}{$_="$.users to date"' is doing:

The -p option wraps your code in the following loop (see perlrun):

LINE:
  while (<>) {
    ...             # your program goes here
  } continue {
    print or die "-p destination: $!\n";
  }

The code supplied with the -e switch inserts a closing curly brace, creating an empty while BLOCK, followed by an opening curly brace, which makes a bare block after the while block.

LINE:
  while (<>) { }
  { $_="$. users to date" }
  continue {
    print or die "-p destination: $!\n";
  }

The while loop reads all the input records, the bare block assigns the string including the value of the input record counter to $_, and the continue block prints the string.