My favorite consequence of suid + hard links is that the combination opens a new security hole, where a user can stash away hard links to suid binaries for later exploitation. Of course this has been worked around ad-hoc by at least some package managers clearing the suid bit of the old file when upgrading it.
I am confused by the characterisation of the linux filesystem as a DAG. I suppose that was true on unixes that could hard link directories.
The bit about suid shell scripts is a trifle misleading for linux too, as the kernel does not honor suid bits on scripts. Perl worked around this with suidperl, which proved to be problimatic; perl's taint mode has more general applications (think CGIs).