In short, if you don't see the license, you may *use* the
software for
any purpose (which is allowed by GPL), but you may not *copy* it. If you
see it, you may do whatever it allows you to do.
I agree that certain proprietary pieces of software need EULAs, but
we're not talking about GPL, or most of Free Software licenses for that
matter.
It in part varies by country. The GPL is a copyright license not a contract
and that actually also restricts what it can do.