The customization is still only limited to checking or unchecking the elements in each section.
This customization is absolutely minimal.

What you still cannot do is change the icon size, minimum width of the sidebar, and there is a large margin of wasted pixel space on both sides of the elements within the sidebar. Also the sidebar now always has to show, unlike tiger where you could collapse it into just icons or hide it on the side altogether, while still keeping the top bar. Even if you remove all the items in a section, the section still appears. For example I never use the 'search for' section. Can I remove it? No. I can remove the elements, but the category 'search for' remains visible. What good does that do me?!?

Someone needs to make a program that allows you to fully customize this.
Shapeshifter is a program that can customize the finder interface, but so far it does not support leopard, only tiger. No word on when it will either.

You can change the width of the sidebar by placing your cursor on the edge of the sidebar and dragging.
You can hide the sidebar in any finder window by clicking on the button at the top right of the window.

For those of us with middle-aged eyes, I can't stand the size of the type in the sidebar. I have a cinema display to make things big. nope, can't do anything to the sidebar. It was sized ok for me in Tiger. why the teeny type? Also, could drag files over there before. I have a couple I use regularly - I like the location of the sidebar vs. the location of the dock. i'm forced to use aliases on the left side of my screen like 1999. this is what i call dumbth.