http://www.cupcakeproject.com/2011/04/easter-cupcakes-baked-in-real-egg.html
My concern would be the risk of eating shell/salmonella or does the baking temps clear that risk?
The salt water soak should take care of any issues!!
You could also rinse them in bleach water if you like.
Tami 
Since no buggies live past 160 and you bake at 350, you are 250% fine!
Per the FDA, it looks like egg shells, cooked, must still be treated with the same care that a cooked egg must have. The shell can be used, but only two hours out of refrigeration. It also must not come in contact with contaminates.
The only way an egg, or any part of the egg is completely safe for good is through pasteurization used in plants (low heat). The bleach method is not on the FDA sites for egg safety. So pasteurized egg shells can be used, but regular eggs must be treated like an egg. Over the 160 mark only buys the two hours at room temp.
Additional:
In IMBC/SMBC/FBC, we are introducing sugar, with the sugar actually turning the egg into a confection with IMBC/FBC. The egg shell on its own does not have the protection of the sugar. From the site, it seems that the shell can pick up the same bacteria as an egg. For example, a hard boiled egg, cooked well over the 212 boiling point, can only safely be out of refrigeration for two hours. The information on the shell was the same.
Per the FDA, it looks like egg shells, cooked, must still be treated with the same care that a cooked egg must have. The shell can be used, but only two hours out of refrigeration. It also must not come in contact with contaminates.
The only way an egg, or any part of the egg is completely safe for good is through pasteurization used in plants (low heat). The bleach method is not on the FDA sites for egg safety. So pasteurized egg shells can be used, but regular eggs must be treated like an egg. Over the 160 mark only buys the two hours at room temp.
Susan, I bet this applies for hard-boiled eggs. The inside of a hard-boiled egg is still considered perishable. But it's illogical to call filling an egg shell with a non-perishable food, like cake, then cooking it at over 200 degrees past what the FDA considers pasteurized for 15 minutes or so (when the FDA only requires 1 second at 161 to be "pasteurized") then reclassify it as a perishable food. I don't believe it is. The shell is inorganic and bacteria lives only on the surface, and no bacteria lives at 350 degrees.
I know when I was a kid I used to eat hard-boiled eggs that my parents used to leave around the house on Easter hours and I can't recall anyone ever getting sick. After we kids would find all the eggs they would sit in a bowl on the dining room table literally all day for us to snack on. Those things would be out for 24 hours or more!
Man, those were different times 
Anyway, there must be another rule somewhere because I was just at CocoBella, a very popular chocolate store here in SF, and they were selling chocolate eggs - real egg shells that they filled with various flavors of chocolate ganache, basically turning them into very large bon bons. No refrigeration. No special handling. I even asked if they were real egg shells because I had never seen that before. I almost bought one because I was intrigued but skipped it because the line was super long!
Pasteurization and boiling are different. The FDA sites all say that safety is only low heat pasteurization. I know the whole magic 160 degree thing, but that's on an egg. The product must still be treated as perishable, just not dangerous.
I am sure there may be processes that can render the shell free of danger, but I don't see anything that says it's anything but pasteurization. I don't see where the home or commercial baker can duplicate the process and be sure that it is safe for commercial use.
I'm sure that places can get pasteurized egg shells. A plant could do it for a distributor. But there is nowhere that states the shell is safe without this process.
This is just like the threads about the egg containers. People came on there and said bleach would make them safe, but the government clearly states pasteurization and nothing else.
We can all take the risk or try to rationalize. I agree it makes sense. But only a select few are succeptible to the dangers of eggs. With so many precautions on the egg board and the FDA sites, not one place gives an alternative. That means that those who choose to use these products have no leg to stand on if a tragedy occurs. I'm not willing to sell a product that clearly gives no alternatives to safety. I may put raw eggs in my Key Lime Pie and milkshakes and eat cake batter, but I don't serve them to my pregnant daughters and I don't sell it.
I guess my point is that on eggs, meat, seafood, dairy, and many other foods, there are government sites that give us the information we need to make food safe and that act as guidelines to limits and minimums. If those sites do not address the process or they give no alternatives to the standard process, you cannot be sure. It will be a guess. I'm not selling a guess.
We have quite a bit of property and assets, as I'm sure no one reading this wants to lose their hard earned assets for a cupcake in an eggshell. Why go against the standards set forth on the numerous .gov and official sites and set yourself up for liability?
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