Cannot reproduce here. I've never seen anything like that. However, don't confuse Working Set and Private Working Set.
Working Set includes data which is shared between processes, like DLL files for which the same version of the DLL is used by multiple programs. So if your program only uses 15 MB of data itself and it depends on 50 MB of DLLs that are already loaded by the system, the Working Set shows both those figures combined; the Private Working Set only shows the memory that is actually consumed by running that process. So in other words, if you terminate that process, the Private Working Set memory always becomes freed-up, but the rest of the Working Set memory (probably) doesn't, because other programs are also using those resources.
That said, if you're seeing more than ~150MB of data in your private working set for both explorer and dwm, it is most likely a driver bug with your AMD drivers. Make sure you've got the latest ones; and if you do, try downgrading to the immediately prior version. Right now I think that's Catalyst 12.6 for the latest and 12.4 for the immediately prior.
This sounds like a memory leak, or you have an absolutely enormous screen size (6 monitors at 2560x1600 each or something crazy like that). I have a dual monitor system with a total of 2720x1924 resolution, which is 5,233,280 pixels... if the color data for one pixel is 32 bits (4 bytes), that means that storing one complete uncompressed image of my framebuffer requires 20,933,120 bytes, or almost 21 MB. Yet dwm.exe is using 13 MB of private working set, and 35 MB of total working set, with about a dozen windows open and all effects enabled, including minimize animations.
BTW, the framebuffer would occupy 589 MB for a single frame if you did have six 2560x1600 monitors, so even then your dwm memory usage is incongruous with your screen size, since my 21 MB framebuffer only eats a relatively smaller 13 MB of private working set in dwm.exe -- and I'm sure a lot of that is stuff like HLSL shaders for the glass effects and various DLL libraries and stuff. Also, my dwm memory usage doesn't increase when I minimize an explorer window.
Do you have any Explorer shell extensions or customizations installed? Maybe WindowBlinds? Just taking a stab at it. A bog standard graphics driver with a bog standard explorer and system DLLs just shouldn't do that. Did this start happening after you did something to your computer, or has it been like this out of the box?
Yeah. This is probably a driver bug.