Hooray, someone who actually has some decent knowledge on computing!
Just a few points I'd like to add.
Memory: Vista (and XP too from memory, maybe not as in depth though) allows you to display active/inactive memory plus a bunch of other stuff through the task manager. It isn't viewable by default, but you can add the columns to the display for all sorts of stuff related to processes.
Security & backwards compatibility: I'm lumping these together because in windows these are actually closely related (from a Windows point of view). Microsoft is between a rock and a hard place when it comes to these. While I agree there are better solutions than what they are doing, they are in the awkward position of offering full backwards compatibility so their big customers remain happy, while trying to introduce a better security model, often at the expense of backwards compatibility. While I am sure there are plenty of people that would like to give away a large amount of BC for security, many of these customers aren't buying 1000s of windows licenses.
Kernel: Just a side note, the next installment of windows is supposed to be a complete overhaul to have a genuine microkernel (once again).
Managed Code: I'm unsure what you mean by MS will be unable to check code is safe to run if it is managed. In a correctly managed environment, buffer overflows etc... are not an issue because the (should) VM handles these problems.
64bit: Just add, the minimal slowdown which occurs when running 32bit apps in a 64bit environment is usually due to the processor switching from long mode to protected mode (and vice versa). And to nitpick, the directories you have (while thats how they should be) are wrong. System32 is where the 64 bit dlls go, and SysWow64 are where the 32bit dlls are stored. Retarded much? This is one of the dumbest things I have ever seen.
DX10: I'm surprised you'd still be having issues these days. A lot of the issues before were because ATI and nVidia's drivers were absolutely terrible under Vista. While there still may be the odd slowdown due to dx9 called being wrapped, there shouldn't be any major issues. While I still have XP installed on my system, I pretty much do all my gaming under Vista now (I have a 7900GS) and get more than acceptable framerates.