. in $path

[Andrew Hume]

research unix has su in /etc, not bin, and as /etc is not normally
in $PATH, you get into the habit of saying /etc/su real fast.
as for system v style machines (like sgi), su is a botch in that it
is in /bin but i always invoke it directly as /bin/su.

it seems this is the only program that people quote as a real problem;
always invoking it as a full path seems preferable to not having . in $PATH.