This is a bit of a protest since I got all excited about doing some WebGL goodness with native client, but then realised that whilst 3D is the very first thing on the features list, it isn't actually supported any time soon:
"Run native code modules that render 2D and 3D graphics" http://code.google.com/chrome/nativeclient/
Later on they even say "This capability enables demanding applications such as console-quality games" ... oh they rub salt in the wound!
So maybe you can all dive in and find things that are computationally too heavy for JS but are not 3D and not serverside?