One thing that bugs my mind lately is: which architecture Intel Core Duo uses? If we read this Wikipedia entry, one will quickly conclude that it is "enhanced" Pentium M.
So, does gcc agree with it? Not really. Using the idea taken from this blog entry, Core Duo is a Prescott! Here's the output:
/usr/lib/gcc/i486-linux-gnu/4.4.3/cc1 -E -quiet -v - -D_FORTIFY_SOURCE=2 -march=prescott --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=generic -fstack-protector
Surprisingly, this is indeed correct. Gentoo's wiki page support this, even Intel's engineer puts amen.
Summary: I conclude, Core Duo it's Yonah (Pentium M), but optimization wise, assume it's Prescott.