I can tell you that the Apple Smart cover will put the iPad to sleep and wake it as it did with the iPad 2. 3rd party cases, however, seem to have lost that ability.

My sister and I both pre-ordered iPads, she ordered the smart cover with hers, I ordered a case from Amazon that claimed to have the sleep/wake function. Hers worked, mine didn't. I'm confused.

I think the sleep/wake function is depend on the pole of magnet , the location is as ipad2. You'd better get one new smart cover for new iPad.

just tested smart cover from ipad2 on the new ipad3 and it worked totally fine!

I have a smartcover for my iPad 3rd gen and have no trouble with it. It even fits in a BookBook cover from Twelve South. I use them together so that I know that my iPad goes to sleep and wakes properly. .

My puro smart cover did not work with my new ipad3. I read the ipad3 uses a different magnetic field sensor that is sensitive to magnetic field direction. To test this I removed the cover from my ipad and positioned it to the right op my ipad in portrait mode, the lid opening to the left. When I opened it, the edge of the lid covered the right edge op my ipad and voila, the ipad switched off. The malfunction of my puro was caused by the position of the magnet. I then cut a 1 inch opening thru the stiches of my cover some 3 inches from the top, pulled the round magnet using a pincet and put it back in upside down. When I tested the cover, it worked fine. A few stiches and the cover was good as new. Wish you happy sewing.

I have a smart cover from my older iPad 2, and it works fine on my iPad 3, sleep function and all.