SUID directories -- security concern?

[Guy Harris]

 >>I've never seen any code to make use of a SUID directory, ...
 >
 >It can't be set-UID.  Probably if it has a meaning (which I cannot tell
 >without access to your system source) it is "only the owner is permitted
 >to remove entries from this directory".  That sort of thing is a fairly
 >common extension to the standard UNIX file permissions scheme.

The common extension of that flavor with which I'm familiar uses the
"sticky bit" rather than the set-UID bit - at least it does in 4.3BSD
and System V Release 3.2.