Not sure if you were aware or someone else has mentioned this, however

has a track record with Mac OS X release as such:
10.0 = initial beta refinement over Mac OS 9
10.1 = features and improvements
10.2 = speed and refinements
10.3 = features and improvements
10.4 = speed and refinements
10.5 = features and improvements
10.6 = speed and refinements
10.7 = features and improvements
10.8 = speed and refinements
Users of OS 10.x and pre 10.x have know this for a while. The question mark in all this is if Core2Duo will be supported under Mac OS 10.8 or will it drop support until 10.9. I have a hunch that 10.8 will be the last OS update to be supported on Core2Duo machines.