One of the girls laid a soft shell egg the other day & it gave Koo a bit of a shock when she was collecting the eggs :D We have only ever had 3 or 4 of these over 16 years & 3 lots of chickens..
A soft shell egg can be a one off or in some cases caused by stress, a sign of nutrient deficiency or illness in the bird.. In our case I think it has to do with the age of our 2 older chooks, Greedy & Chicken Little.. If there is a continuing problem we will be off to the vet with the young lass in question..
I have come across a few great sites & forums that have been useful over the past few years.. Backyard Chickens is one forum that has some great posters & information like this page on Common Egg Quality problems..
The Chicken Vet from the UK has also got some great information on diseases on his site..
Cheers & hope the info helps some folks out there,