I think my thoughts have all be articulated by others now.
Basically it turns out it isn't so easy to figure out where you draw the line when you say that someone doesn't have to do something against their principles (particularly those sourced from a particular religious teaching).
We seem to all agree that a minister/priest of a church does not
have to perform the
religious service of marriage.
We seem to also agree that someone working to supply some service must not discriminate. E.g., pharmacist, someone renting etc.
Then we can start to discuss individuals in roles "between" these. I think it's been discussed enough by now but we haven't, that I noticed, drawn up the conclusions of the "court". It maybe that this will have to be worked out with a variety of court cases to settle it.
Perhaps the guiding principle is:
If you can't discriminate based on race, religion etc. then you can't discriminate based on orientation
unless you are offering religious services. That should be the criteria since the law was written to specifically allow discrimination from religious organizations.
Here in Canada, with gay marriage totally legal across the country I think there have only been a handful of issues that have arisen. It's been pretty quiet overall and seems to be working so far.