In Howard Hansen's EXCELlent review of Excel 4 in TidBITS-127, he makes the following comment about the pop-up menus feature:

When you hold down the command and option keys and click the mouse, Excel brings up a pop-up shortcut menu right next to your mouse pointer. Select a range of cells, command-option click, and Excel allows you to instantly cut, copy, paste, clear, delete, or insert, as well as change number, alignment, font, border, or patterns formatting. This saves the trouble of mousing all the way up to the menu bar, finding the right option and choosing it. (I find our ever-increasing computer laziness quite wonderful!)

Unfortunately, pop-up menus are inherently more difficult and slower to use than are pull-down menus. This is due to Fitts's (1954) Law, which governs hand and arm movements. The application of Fitts's Law is discussed by former Apple interface guru Bruce Tognazzini (1990, May) and by Walker, et al. (in press). Fitts's Law essentially states that more precise manual motions must proceed more slowly than coarse movements.

The reason for this is that you can mouse off the top edge of a pop-up menu, but you cannot mouse off the top of the menu bar. This "impermeability," as Walker, et al. call it, makes the menu bar essentially an infinitely tall target. The user can therefore program a very coarse, quick movement for the mouse hand to access the menu bar.

One heuristic that might improve pop-up menus is to cause the most recently used command to be the one that comes up under the mouse pointer. However, unless Excel 4's menu structure is so complex that it requires a great deal of cogitation to recall the locations of the common commands that pop up, the drawbacks of pop-up menus will very likely overwhelm the benefits. Moreover, by the time a user of Mac Excel 4 remembers to and does press the command and option keys, she or he could likely have moused up to the menu bar and chosen the appropriate command.

Now, it is altogether possible that the pop-up menus in Excel 4 do make it quicker and easier to use, but it is not for the reason Mr. Hansen proposes.

References:

Fitts, P. M. (1954). The information capacity of the human motor system in controlling amplitude of movement. Journal of Experimental Psychology, 47, 381-391.

Tognazzini, B. (1990, May). Pull down menus win hands down. Appledirect, pp. 25-27.

Walker, N., Smelcer, J. B., & Nilsen, E. (in press). Optimizing speed and accuracy of menu selection. International Journal of Man-Machine Studies.