Mark,
According to the yeast producers, once you get above 1% salt (by weight of flour), it has an inhibiting effect on the yeast performance. However, if you have a proper balance and quantitative relationship between the salt and yeast, you should get acceptable results. It is when there is too much salt in relationship to the yeast that you can get in trouble.
The way that Craig deals with salt and yeast is the correct (and recommended) way for a natural leavening system. You can do it the same way if using commercial yeast (fresh or dry) although instant dry yeast (IDY) and fresh yeast can be combined with the flour (that is, they don't have to be rehydrated). The one thing you normally don't want to do is to add the salt and yeast to the water all at the same time for other than a very brief period since, as the article at
http://www.kingarthurflour.com/professional/salt.html discusses, salt can have a retarding effect on the yeast because of the way that salt can leach liquids (including glutathione) out of the yeast cells. The best and safest way to do it is to let the salt hydrate directly in water and then add the leavening agent (if it is to be hydrated) when there is very little likelihood that the salt will leach out yeast cellular fluids. Having said all this, there will be some people who will say that they throw the salt and yeast into the water all the time, without any ill effects. However, often, after careful scrutiny, it turns out that the yeast levels were higher than normal and could survive some losses, or the interaction between the salt, yeast and water was momentary. Using far more yeast than necessary because of high salt levels is a matter of poor recipe design in my opinion, whether intentional or out of ignorance.
As for when the salt is added to the dough, sometimes salt is added to the dough toward the end of the dough kneading process if the flour is a strong flour. Otherwise, the dough may be overly strengthened by the salt. French bakers also added the salt later in the process. They weren't concerned with the fact that doing so caused the the dough to be bleached out by oxidation of the dough, which would have been prevented if used up front (because salt is an antioxidant). Salt is also added later in the dough making process when an autolyse is used. However, whichever way the salt ends up in the dough, it will act as a regulator of the fermentation process. But so long as there is a proper relationship between the salt and yeast as mentioned above, the results should be acceptable.
A final point to make is that modern yeast strains have been developed that are more resistant to salt levels. But I wouldn't use that improved resistance as an excuse to abuse the yeast or as an excuse for poor recipe design.
Peter
