libata drivers (/dev/sd*) replaced /dev/hd* a long time ago, support for hd* rules was removed upstream at udev-148. But app-admin/hddtemp/files/hddtemp-conf.d was not updated since 2006 and still has HDDTEMP_DRIVES="/dev/hda /dev/hdb" Please replace it with HDDTEMP_DRIVES="/dev/sda /dev/sdb"
Thanks! Fixed. + 16 Mar 2012; Amadeusz Żołnowski <aidecoe@gentoo.org> files/hddtemp-conf.d: + Use long options and set /dev/sd* by default instead of /dev/hd*. Fixed bug + #408269 and bug #390275 btw. +