I was instantly frustrated by the amount of padding on the new Gmail look (released to me on Nov 2nd, 2011). Turns out it's quite easy to fix. Just click the "Gear" button (the lower one, not the top right corner). And choose from the fuzzily named Comfortable, Cozy, or Compact. Personally I prefer Cozy or Compact, but Comfortable is probably only suited if you either have a 40 inch monitor or are legally blind.
Remember to check out my post about cool shortcuts in Gmail and Google!