I've been wondering about it ever since I noticed that many dir permissions in AAT have a 't' where one would normally expect an 'x' for 'others'.

man chmod 't' is "save program text on swap device"

I've never seen a 't' before and man's explanation doesn't help me understand it.

Can anyone shed some light on 't' usage and explain why its helpful/needed for AAT ?

None that I know of. What dir had that?

/backup
/config
/templates_c

It was that way right after I tar zxvf the aatrade20 tar.gz file.

Same 3 dirs have 't' in AAT v.014.1 also.

Must been something in the way PJ tared up the files and dir. They are not nessasaary.

Nothing on my end. All directories were tared up the same way. Since those directories are directories the admin had to manually set to writable before you can even run the create_universe.php I would say something they did in chmoding them caused it.