lead_org's idea of useing a credit-card or similar tool to spread the compound is a good idea.
My idea of iceing on a cake was a bit vague I suppose. The point was an even thin layer, liberally applied to fill the neccesary imperfections, yet thin enough to not be wasteful.
This excerpt from the Wikipedia artical on "Thermal Grease" may enlighten things a bit for all in question. There's more for those technically interested on the Wikipedia web site; referrenced via the link above, but I think the notes below should suffice enough info for the average person.
Purpose
Thermal grease is primarily used in the electronics and computer industries to assist a heatsink to draw heat away from a semiconductor component such as an integrated circuit or transistor.
Thermally conductive paste improves the efficiency of a heatsink by filling air gaps that occur when the irregular surface of a heat generating component is pressed against the irregular surface of a heatsink, air being approximately 8000 times less efficient at conducting heat (see Thermal conductivity) than, for example, aluminium, a common heatsink material.[2] Surface imperfections inherently arise from limitations in manufacturing technology and range in size from visible and tactile flaws such as machining marks or casting irregularities to sub-microscopic ones not visible to the naked eye.
As such, both the thermal conductivity and the "conformability" (i.e., the ability of the material to conform to irregular surfaces) are the important characteristics of thermal grease.
Both high power handling transistors, like those in a conventional audio amplifier, and high speed integrated circuits, such as the central processing unit (CPU) of a personal computer, generate sufficient heat to require the use of thermal grease in addition to the heatsink. High temperatures cause semiconductors to change their switching properties to the point of failure while CPU power dissipation overheating causes logic errors as heat raises electrical resistance on the multi-nanometer wide circuits of the CPU core.[3]
Applying and removing
Computer processor heatsinks utilize a variety of designs to promote better thermal transfer between components. Flat and smooth surfaces may use a small line method to apply material, and exposed heat-pipe surfaces will be best prepared with multiple lines.[4]
Because thermal grease's thermal conductivity is poorer than the metals they couple, it is important to use no more than is necessary to exclude air gaps. Excess grease separating the metal surfaces further will only degrade conductivity, increasing the chances of overheating. It should also be noted that silver-based thermal grease can also be slightly electrically conductive. If excess were to flow onto the circuits, it could cause a short circuit.
The preferred way to remove typical silicone oil-based thermal grease from a component or heat sink is by using isopropyl alcohol (rubbing alcohol). If none is available, pure acetone is also a valid method of removal. There are also purpose made cleaners for removing and purifying the surfaces of the contacts.
HTH..... 
Regards,
Visible_Spirit
