Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
I'm do as well usually keep mine about 4 years . Hopefully the timemachine backup on the Mac helps with the switchover. But usually its the little things that have been tweaked over the tears that you quickly miss.
Obviously avoid any new OS for about a year when it first comes out. You don't want to jump into the next Vista or Millennium, plus drivers will be worked out and more hardware will be better supported (and software).