I was intrigued by Deb Tucker's square-in-a-square ruler. Her methods have very little waste, and I like the precision of making a unit a bit oversize and cutting it down. You can obviously do it with regular rulers, too...which is the reason I haven't bought hers yet. But having the marks to easily position the ruler is a nice idea.
However, I realized this week, if you buy a kit you may not have the option to use her method because the kit dictates the size/shape of the fabric provided. But I do like the convenience of having someone else pick out fabrics that go together.