It does go off. AS5 is not the best of the compounds anymore even the generic white paste tends to outperform it. But saying that you will find that there isn't more than about 5C delta between all the pastes. Its worth looking at the reviews, but also be reasonable about the cost because the Indigo solution while excellent is also a rip off.
I was using OCZ Freeze, but it seems to have been discontinued. I upgraded my processor two weeks ago and was about to pop my HSF back on when I noticed the syringe was empty. Went down to the small local computer store and all they had was this:
Its easy to apply with a little brush and I was skeptical at first, but the X4 980 was idling at 32C and load was 49C. After it cured for a week that dropped to 29C and 45C. Pretty pleased with it - it did a bit better than the OCZ Freeze. I'm starting to think any name brand thermal compound properly applied is going to be within a degree or two of each other.
Hardwaresecrets seems to be on a quest to test and round up all the thermal compounds in the world.
Was their latest review. They even test chocolate, toothpaste and diaper oil!