new features of OS X Yosemite are introduced here
I'm stuck with OS X Snow Leopard with my late 2006 iMac which originally came with OS X Tiger. I was always impressed how easy it was to upgrade OS X. If it was possible for me to upgrade further I would do so. Usually there are severel interesting new features available.
iMac is just a perfect computer for whole family for browsing and reading e-mail etc. Saves my nerves compared to Windows PC!