I had the original jawbone - not bad, but never could get very comfortable with it, ear loop was a pain, wore out the ear piece connector.
Got the new Jawbone ICON with the iPhone 4 and LOVE it. As poster above notes, it shows the battery level in the status bar.
So far, everybody can hear me great and the thing fits awesome. They finally (not sure if other versions had this) an excellent method for fitting it snugly in the ear. Literally tried knockin myself in the head and couldn't get it to budge.