I was planning on adding an option to allow the user to select the
icon (haven't had the time yet), which is why you see them both in
there. At the moment the behavior is that if you are on a large
screen device (Droid/Milestone or Nexus One) it will use the eclair
icon, if not it will use the older icon.
If you really want the new icon you can download the source, rename
the icons around and re-build and install on your phone (it won't be
signed with the release key though). I think this will prevent you
receiving updates from Market unfortunately.
Adam
If you need some inspiration, ChompSMS has customizable notifications
with a whole bunch of different colored icons. I think that would be
the best way to go with yous. Just let people choose between recolored
versions of the default 1.6 and 2.1 images. i think everyone, myself
included, would be happy with that.