The kernel option "Dell laptop support" causes PS/2 to stop functioning on Dell Latitude C610. This option has worked successfully on all other Dell models I have tested but after some trial and error debugging I found that this option was causing my built-in laptop keyboard and mouse to stop functioning. USB keyboards and mice worked however. I have tested this option on a few kernels up to the current stable for x86, gentoo-sources-2.6.16-r9. By disabling this option my laptop works fine now, but I wanted to notify the kernel developers of this incompatibility.
Reopen with emerge --info and your kernel .config.