Honestly, his program consists mostly of a long URL. What does he hope to get out of this?

Update: Screw golf, it's not even good code.

• Useless srand.
• What's with the \r\n at the end of the body?
• Specifying both Proto and Type is redundant.
• join would make the code easier to read. Bah, even breaking the long url more logically would be more readable.

The following is so much better, and by his count, it's only 4 lines even though it's practically not golfed:

#!/usr/bin/perl -MIO::Socket
my $body = join('&',
   "vid=$ARGV[0]", 
   "private=0",
   "geolat=".( $ARGV[1] + rand() * 0.0001 - 0.00005 ),
   "geolong=".( $ARGV[2] + rand() * 0.0001 - 0.00005 ),
);
sleep(rand()*600);
print(
   { 
      my $sock = IO::Socket::INET->new(
         PeerAddr => 'api.foursquare.com:80',
         Proto    => 'tcp',
      ) or die $!
   } 
   join("\r\n",
      'POST /v1/checkin HTTP/1.1',
      'Host:           api.foursquare.com',
      'User-Agent:     Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en)'
                    .' AppleWebKit/420+ (KHTML, like Gecko)'
                    .' Version/3.0 Mobile/1C10 Safari/419.3',
      'Content-Type:   application/x-www-form-urlencoded',
      'Authorization:  Basic XXXXXX',
      'Content-length: '.length($body),
      "",
      $body,
   ),
);
$_ = <$sock>;
[download]

I'm not convinced that long User-Agent is required. And you can surely get away with not waiting for the reply. (Could fail, but not likely.)

I was tempted to write the User-Agent as equivalent

      'User-Agent: Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en)',
      'User-Agent: AppleWebKit/420+ (KHTML, like Gecko)',
      'User-Agent: Version/3.0 Mobile/1C10 Safari/419.3',
[download]