WARNING, I work for Molecular Dynamics a (shutter) Vendor!
 
  >Several of the confocal vendors are offering a new option (or are about
  >to...) which should significantly help with laser lifetime. They can now
  >enable computer control of laser power such that it is only brought up to
  >the desired value directly prior to scanning: otherwise it stays in idle.
  >Since the Kr/Ar stabilizes in about one ms, you can cycle it back and
  >forth between idle and active without significant disaster. I know that
  >both Zeiss and Leica are bringing this new cability on-line for the
  >Omnichrome 643 series Ar/Kr. I do not know if the BioRad's ILT laser will
  >also have the same capability.
  >Chip Montrose
 
  Molecular Dynamics and Sarastro before it, have always computer controlled
  laser power.  For most users the laser spends most of its time in "stand-by"
  mode waiting for the investigator to find something to scan or get a cup of
  coffee.  Perhaps this is why we don't see a significant difference in the
  lifetimes of Ar or Ar/Kr lasers (thousands of hours!)
 
  happy scanning,
  david hanzel