Yes, cold frames would be another great way to start seeds. : )
What I like about the milk jugs is not having to monitor them for moisture content. At least not until the warmer weather arrives and there are isn't any rain to keep them watered. Usually by then they are ready to plant out anyway. If there is still danger of frost I use the top half of the jug to cover the individual plants (kind of like a miniature green house. You just have to remember to remove them if the weather gets to hot during the day.
