Ask before performing massive operation on Ctrl+Shft+arrow
We all use Ctrl+Shft+arrow when building out spreadsheets. We all, sometimes, make mistakes and Ctrl+Shft+down to row 1,048,576 and then execute, after which you usually need to force a shutdown.
Excel doesn't ask before performing this very large operation. I'm thinking of something like the dialog box that opens up saying "This operation will affect a large number of cells." That would save us all the once-a-month pain of a finger slip.