[wayner]

A retaining wall concentrates most of the load in one spot vs spreading it over the slope so keep that in mind.

The biggest mistake people make when they put in retaining walls is to not add drainage behind the wall.
Water is extremely heavy so you don't want to create a dam.

Drains at the bottom of the wall, and a layer of stone behind the wall from base to near the top, otherwise they dont last as long as they should.
A fabric barrier behind the stone to keep the dirt from migrating into it.