I appear to have a similar issue to this thread:
In that the SKU field is totally not there, either in the Quick Edit or the full edit view.
I have the product Import/Export plugin, & I note that the field is in the DB, most of my products have a SKU, but I added a few recently & obviously didn't notice the SKU field was missing.
The Import/export plugin relies on the SKU to hand the new data from, as well as it being a generally good thing to have a SKU on your products!.
I'm using 1.6.6 of the plugin & WordPress 3.5.
I note that the similar thread is resolved, there was a "dodgy piece of JS" but there are no more details than that - Hoping for a little more information to help me get my SKUs back!