I kind of agree with this... the placement of the formula entry is not always ideal.
Most of the time it's OK, but sometimes it does obscure the cells I want to reference. The question, though, is where should it go?
I'd think it would be easy enough to make sure the formula entry doesn't block any referenced cells that are already in the formula, but that doesn't account for intended changes (how does Numbers know not to block cells I'm going to add to the formula?).
I also don't want it to be fixed at the top or bottom of the screen since that leads to a lot of mouse movement for large sheets/monitors.
For the record, Excel does something similar - shows the formula over the cell, but it's even worse there since it can obscure adjacent cells and there's no way of moving it out of the way.
For now, since I primarily use a MacBook Pro and a Magic Mouse, I find the easiest workaround is a quick two-finger scroll up or down after clicking a cell. This has the effect of shifting the underlying table up (or down), but leaves the formula bar floating where it was. Different solution to moving the formula bar out of the way, but you don't need to be precise with the cursor position.