Which was caused in part by badly behaving programs (writing user data to the Program Files directory) that triggered the UAC prompt, if I'm not mistaken.

They improved the system in the next release, and since Win7 UAC generally works perfectly even with the "badly behaving" software. Sensitive directories are now mirrored elsewhere in the filesystem, so that when your program wants to read from, say, Program Files directly, what it really reads is C:/Users/[username]/AppData/Local/VirtualStore/...

I've never experienced this in writing my own software. If I try to read or write to a directory I'm not allow to I simply get access denied.

f = open('C:/windows/test.txt')

try:

    f.write('test')
 

except Exception as ex:

    print ex
 

IOError: [Errno 13] Permission denied: 'C:/windows'

Try the same with C:/test.txt. Open Explorer and see if the file actually appears in C:/.

So that's what the policy "Virtualize file and registry write failures to per-user locations" does... uh, good to know :) thanks!

In my particular legacy-apps' field, I believe most problems are due to interactions with the DCOM subsystem though.

Yeah, I only learned about it after I discovered what "~" is being resolved to in my Emacs installation on Windows...

That was already in Vista, if I remember correctly.