I simply can't share nortexoid's opinion on the differences between thermal compounds. Mind you if your not overclocking your processor then it should work just fine with the thermal pad. But realize you will most likely see temps over 50C regularly (maybe over 60C depending on the mobo and unless you have internal thermal diode support on the motherboard you really don't know whats going on inside for sure). I may be wrong, but I believe it is called thermal drift in the chips that actually is the aging factor for most (if not all) semiconductors. And from the simple conclusion that higher temps = shorter lifespans for your processors. You might want to reconsider the term good enough.
From my personal experience with thermal compounds (I did a thermal compound test several months back with my watercooled 1ghz, but that thread dissappeared so I can't point you too it). But I tested Nanotherm, Arctic Silver (ASII, Alumina, and several prototypes), and Radio Shack thermal compound. I did a stability and thermal test with my socket thermistor and a side thermistor. Even with inaccurate external thermistors you could see measurable differences (you have to properly apply and prepare the surfaces - I lapped between each compound to give the compounds the benefit of being the one that matters.) I had a variance of stability of 100mhz (thats a 10% overclock for a 1ghz chip) and a temp difference of 10C between the worse and the best. The worse was Radio Shack the best was the prototype from Arctic Silver. I actually was able to achieve stable overclocks that I previously was unable to reach with the prototype.
Anyway the moral of the story was the Radio Shack compound destabilized and was drying out after only 6 hours of testing, so be careful when you choose your thermal compounds because they really do make a difference, at least in my experience...........
P.S. Thermal pads have a much worse thermal conductivity even than Radio Shacks thermal compound, but at least have stability (don't dry up). So I can only recommend the use of a thermal pad if your NOT going to overclock.
And if cost is really the factor then go with the Alumina from Arctic Silver, it has decent - great performance, isn't conductive and is very reasonable.