So .... according to stat(), all directories on my windows Vista box (even those that I can't write to) are drwxrwxrwx. Does this signify some shortcoming of the stat function on Windows ?
Yes. Windows uses ACLs, not the Unix idea of owning user, group members, and other people (u,g,o). stat() emulates just enough of the Unix idea to allow common programs to work. It pretends that everything is readable and writeable for everyone. Finding out that things may be read-only or even write-only is left to other functions like open, read, and print. If you would run on a Unix system with ACLs, you would have exactly the same situation. The mode information returned by stat does not know about ACLs, and even if stat() tells you a file or directory is readable or writable for everyone, the ACLs may prevent you from reading or writing.
Actually, stat() returns some useful information:
(Strawberry Perl 5.10.0)
As you see, the directory flag is correct, and the X-bit is only set for directories and executables (determinated by the file extension). So, -f, -d, and -x work as expected.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)