Seriously... I use C4D and other big media tools and yet none of them have the atrocious memory management that has plagued AE since day one.
Every AE artist knows that you have to constantly flush the RAM cache to keep AE clipping along nicely while designing. But in versions previous to CS5 it was limited to a 3GB RAM partition. So, even though AE would start to choke itself off, it rarely affected anything else running. But now that they've opened CS5 to 64-bit, it steals every little memory resource on your machine that it can get its grubby little hands on. Oh... I know.. you can tell AE how much to leave for other apps, but I'm not sure if that's a real preference or just something you can adjust to give yourself the illusion that AE will allocate RAM for other functions besides AE. But the real clincher isn't even this... it's the fact that AE keeps items cached in memory that will never be used again within the render... yet for some odd reason, AE engineers have decided that "Hey!... let's try to keep everything that's ever been rendered in this comp in memory!... even if that means it will choke AE and other resources down so low that this mighty machine is brought to its knees!".... and the best part? I'm not even using the multi-core functionality because I'd hate to see it snuff this box completely out of existence.
Note to Adobe... go headhunt some of the programmers out from Maxon.... for some odd reason they know how to write for 64-bit apps AND, more importantly, they understand good memory management.