I do chambers as standard unless I am asked otherwise. A light bass is a bliss so I make it a point to build light basses. My basses weigh 7lbs and below - the lightest being 5.2lbs.
Chambers are important to wight reduction but they are not the only way. Body thickness has a considerable impact too and so do contours. I use a combination of all three.
I have tried a few styles and decided that the almost hollow body way is not for me and that other ways were boring to make
This is the way I chamber a body. It works for me and I'm having fun
The lay out changes for each build, depending on how much weight I want to shed.
I am not sure about the impact on tone though and I would agree with Musiclogic. Even chambered a solid body does not behave as an acoustic one.
I have noticed a slight difference only on one heavily chambered body, but only when playing the bass unplugged. It might just have to do with slight vibrations my chest picks up from the body. But that's just speculation. As soon as the p-ups kick in that too disappears.
edit: and lets not forget the electronics cavity. Some are so large that one can save more than 1lbs on that alone.