>I need advice on ordering Queen Cells that require shipping from a commercial breeder.  What is the percentage that I can expect of Queens who will emerge healthy.

Nobody can really answer that question.  There are many variables:  

the breeder's experience and expertise
luck (viruses, mistakes, fumbles, etc.)
the season and conditions in the hives used to raise the cells
weather and flow conditions
the stock being used
the distance and time from source to installation
the method of transport and temperatures, shocks, etc., 

how your nucs are prepared
where on the comb you place the cell
weather and flows when you introduce
the strain, age and health of the bees in your nucs or hives
availability of your (and nearby) drones and their fertility
mating weather
bird and dragonfly predation of flying queens
your experience and expertise
unknowns and imponderables

That said, you have had some good answers that provide a feel for the possibilities.

In my experience, success can vary from near zero to near 100%, but a safe average with good probability is around 70% IMO.

As with anything, a Plan B is essential.  It takes two or three weeks for a failure to show, unless the problem is simply failure to emerge, which is easy to remedy, especially if you stage sucessive cell arrivals so that you have replacements for duds arriving in waves.  Otherwise, using the duds as seconds or boosters is a possibility, but will you do if you hit one of the near-zero success eventualities?  Hedge your bets.

I have documented some of my experience at honeybeeworld in my diary.  Here is one page http://www.honeybeeworld.com/diary/2000/diary072200.htm

I'll try to straighten out more links.

There are other references, but I am having trouble Googling them.  I think I had better look at my robots.txt.

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