I just tried to use the array formula:
{=SUM(IF(A1:A65536="",0,1))}
to count up the non-blank cells in column A.
Excel helpfully translated A1:A65536 to A:A and then gave a #NUM error.
Using
{=SUM(IF(A1:A65535="",0,1))}
(omitting the final cell from the range) works fine!
Is this a bug or a feature ?
Ian.