Does PAC Validation Require External Communication?

[Michael B Allen <mba2000@ioplex.com>]

This link claims MS' PAC verification can require communication with
the DC:

http://blogs.msdn.com/spatdsg/archive/2007/03/07/pac-validation.aspx

Is this true? If so, services will not be able to authenticate nearly
as fast as they otherwise could.

Mike