Anyone thinking of upgrading from Core Duo chips might as well wait for Ivy Bridge in April. I dont think you can call Ivy Bridge an 'in between'. What with pci 3.0, Tri-gate tech and lower power comsumption, its worth waiting a few months.
That's me. Upgrading every other "Tick" seems sensible - the teething problems with the new architecture are fixed, and you get a die shrink (lower power) too. Wolfdale -> Ivy Bridge for me.