Nobody big is doing it the way you suggest (non-persistent). And once it's persistent, Perl is really quite zippy. Here is a trivial example (Hello world) but probably about as valuable as any benchmarks that don't compare real world use-

use Benchmark qw(:all) ;

my $count = 1_000;

cmpthese($count,
         {
          'C++' => 'qx{curl -i http://localhost/cgi/hello.cgi}',
          'Perl' => 'qx{curl -i http://localhost/cgi/hello2.cgi}',
         });

__END__

Perl under FCGI. C++ as plain executable.

# first run
      Rate  C++ Perl
C++  340/s   --  -5%
Perl 360/s   6%   --

# second run b/c the first seemed too good
      Rate  C++ Perl
C++  287/s   --  17%
Perl 246/s -14%   --
[download]

When someone says Perl is slow, always check the context and take it with a grain of salt. What makes a web app slow can be unrelated app code (DB, network, server, etc). Also, what dragonchild said. Server slots are cheaper than developers.

update: added a missing apostrophe.