Mountain Lion is due for release sometime this summer, but I was disappointed to read in Mac Format recently that neither my Macbook (2007) nor my iMac (2006) would be able to run it. Apparently it is unlikely that Macs made before 2008 will be able to run Mountain Lion even though they may have the core two duo processor.
I just got around to checking, and our Core Duo MacBook also fails to meet the requirements of Mountain Lion. So I guess that in another two or three year time we will be trying to assess whether the iPad has reached the point where it's not worth buying another laptop.