Not all "Thermal Gunk" has been created equally. The grease that came with your heatsink should be fine for general computing provided you clean your CPU and Heatsink of the left over grease residue and oils (from your fingers). Then reapply like mentioned above.
However, if you OC, it would be worth the $8.00 or so to purchase a tube of Arctic Silver compound. Its thermal properties are far superior to the stuff that comes with most hsfs.