To add to the sampling of laser experience:

   We used an Argon laser fairly heavilier for about 5 years and it
was still functional when we replaced it with an Argon/Kryton about
3 years ago.  We are now on our 3rd Argon/Krypton and the newest one
that was just installed came with a "reading" of 600 hours on it,
and I haven't yet been able to determine if that means 600 hours of use
on the tube or not (I wont mention the company that supplied it, they're
still trying to help me with this).  This newest laser was made by
American Laser and they are apparently now reducing the blue line and
increasing the red line, so that as the laser ages, and the red fades,
you will still be able to do double labelling studies effectively.
However, the end result for us is that now we need to use a lower
degree of filtering (a +0.5 log step... we dont have a convenient way
of doing smaller filter steps) and are therefore lasing our specimen
harder than we used to (we do almost all our work with the 488 line).

Don O'Malley
SUNY Stony Brook