nforce-net will probably be removed from portage sometime soon. Could someone please update the handbook, which currently says that nforce-net should be merged for nforce-based network controllers (section 7e, http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=1&chap=7). The reason for removal is that an in-kernel driver now supports this hardware. Its called forcedeth (CONFIG_FORCEDETH). In menuconfig, it can be found under "[*] EISA, VLB, PCI and on board controllers" and is labelled "Reverse Engineered nForce Ethernet support". I'll leave it up to you if you wish to update the documentation making a reference to this change.
Fixed in CVS.