The kernel of the installer CD has CONFIG_ATH9K enabled, but not CONFIG_ATH9K_PCI. That Atheros chipset is very popular on notebooks these days (Apple, HP, Asus). And they all use the PCIe version. Without that option the wireless won't work on these laptops. And Netbooks usually come with no Ethernet.
I had to resort to SystemRescueCD to install Gentoo on several laptops for exactly this reason.
*** Bug 427804 has been marked as a duplicate of this bug. ***
Please test the latest iso as it should include support for ath9k_pci.
 - http://distfiles.gentoo.org/releases/amd64/autobuilds/current-iso/install-amd64-minimal-20120917.iso
Tested. Works as expected. Thanks a lot!
Closing per last comment.