Yeah it's definitely 3/8th. Or at least what I am removing from the wall is thicker than it is, and it measures 1/2" pretty darn closely.
That's fine I can write off this sheet, its not like 2 bucks is gonna break my bank (although 4 bucks might!). As to getting those 2 x 2 squares, I saw them too and was pondering it, but considering that I can pick up damaged boards for 2 bucks or less depending upon how large it doesn't seem cost effective to buy pre-cuts.
As for Jeffc, I hear what you're saying but I don't happen to have any curved surfaces and noise reduction isn't a concern for me.