I would just add that using a polarizer on anything wider then a 35mm lens is going to be problematic.
Uneven blue sky is very common when using a polarizer with a wa lens.
Also a very good tip bellow if you use LR or ACR, use the masking in the sharpening with the alt key pressed down until the sky goes black, so the sharpening will not be applied to the sky. I do this all the time.
Another tip, or something worth trying is on the A77 shoot at ISO 50 and see if the sky looks any cleaner.
johnstra wrote:I thought I had replied already but I cannot find my post so here we go again.
I can now see the problem but it is not always present. I could not find it in the shots I took with the 28-75 and old 2 stop Hoya polariser. However I have seen it in a shot I took yesterday with the 16-80CZ and a Hoya HD. It is not as apparent as in David's shots and I am sure he is right in that we don't get those really deep blues here. I can't find the pic right now to post it but what I find is that I cannot see the fault if the sky is not sharpened. It is also worse if the colour noise reduction is set too low. I find that the default of 25 is about right for that. So in Adobe Camera Raw using Photoshop or Lightroom I use the masking slider (press ALT while sliding to see the extent of the masking). I used around 50 on my shot. This fixes it and generally you do not need to sharpen a sky. I don't know if that will work in your cases but it's worth a try.