I don't even know how to debug this-- or even if it needs debugging-- as I don't know how to tell the difference between how Wine would act if the libraries cannot be found because of a lack of this update, and how Wine acts when the environment has been correctly updated.
My $.02 is if you're crazy enough to use a distro that requires everything to be compiled from scratch, then you better be capable of understanding everything that entails. The same goes for anyone compiling Wine from source. If that means editing /etc/ld.so.conf so the linker can find your libraries, then so be it. Otherwise, it's best to stick with the binaries.
Maybe we need to collect things like this into a "Release Notes" page on the wiki? In this case it would look something like, "GENTOO USERS: After placing the bullets in the chamber, pointing the gun at your foot, and typing emerge you'll need to make some small changes. As root, type "(echo '/usr/local/lib' >> /etc/ld.so.conf) && ldconfig -v".
WTF is with /var/tmp/portage/wine-20050930/image//usr/lib ...
-Brian