Minor edits, for clarity, February 15, 2006.
Here is my two cents worth.
I can't compare the "thickness" of Ceramique with AS5 because I've never used AS5. Compared to AS2, Ceramique is much "thicker", or perhaps more accurately, more viscous.
But before you use the stuff, read on...
I've used AS Ceramique on at at least six processors (four Socket A AMD Athlon XP CPUs and two S754 Semprons) and familiarity is most decidedly breeding contempt. On Socket A it is OK provided that you are willing to put up with its tendency to form "strings" as you pull the tube away from the top of the processor core after applying the compound. Those "strings" can be messy and flop over onto areas of the processor other than the core or heat spreader - hello cleanup (at least if you are as meticulous about this aspect as I am). Also it is not easy to spread the compound evenly over the heatsink which I believe is supposed to be done (the compound should be applied to both the core/heat spreader AND the part of the heatsink that will be contacted).
When you remove a Socket A (or Socket 370) processor that has been applied with Ceramique, the removal isn't very difficult because the Ceramique doesn't tend to glue the heatsink to the processor core due to the small areal contact between the core and the heatsink (for Socket 370, I'm assuming a Coppermine core which is roughly the same size as a Socket A processor core manufactured using the .13 micron process, but definitely not an earlier, larger S370 core or a Tualatin core with its heat spreader). So you can first remove the heatsink, lift the processor retention lever, and remove the processor -- normal procedure. And if the processor does stick to the heatsink, gentle rotation of the heatsink should suffice to break any core/heatsink bond and could probably be done while the processor was still in the socket (I've never had to do this when using Ceramique with Socket A processors).
BUT on heat spreader equipped processors that fit into a socket that is recessed due to the surrounding plastic bracket for retaining the heatsink (as in S754, S939, and many P4s), I absolutely do NOT recommend Ceramique. In these combinations (heat spreader CPU combined with 'recessed' socket) the much larger areal contact between the heat spreader and heatsink gives AS Ceramique the opportunity (which it seizes upon after "setting up" after two or so weeks) to start acting like a blooming bonding agent. Due to the lack of space between the heatsink and the surrounding bracket, it is not possible to rotate the heatsink back and forth horizontally in an attempt the break the Ceramique bond. So as mentioned in earlier posts, when you remove the heatsink, out comes the processor as well, stuck solidly to the base of the heatsink - definitely non-standard procedure. Then you have to rotate the processor back and forth in a semi-circular movement, holding the processor carefully at its edges, to get it to break free of the heatsink. Perhaps application of a solvent and/or heat would make this easier but you can't apply a solvent until the CPU and heatsink are out of the socket. After the processor breaks free of the heatsink, you have a shallowly grooved circle in the base of your heatsink (my experience with a retail AMD all-aluminum S754/S939 heatsink). And hopefully you haven't bent any pins or damaged anything else (like the socket or the retention mechanism) during the entire nerve-wracking process.
Perhaps removal could be facilitated by (1) first removing the retaining bracket, allowing one to rotate the heatsink to break the Ceramique bond (but what if the processor comes out of the socket during this process and pins get bent or you damage surrounding capacitors?); (2) overclocking the processor and running PRIME95 for 30 minutes or so in an attempt to heat up the heatsink and particulary the Ceramique so that it becomes more like syrup and less like bondo, then quickly attempt to remove the processor without it sticking to the heatsink or (3) use a heating device to warm up the heatsink and the Ceramique followed by hopefully the "clean/standard" removal of the processor. But why should it be necessary to bloody overclock your processor or use a blowtorch on your heatsink just to remove a processor - huh?
Have I missed something?
I have used, and liked, AS2. But thumbs down on Ceramique.