No, not entirely in function and certainly not in speed. For instance, opening up a sub folder in a folder in the 2nd HD; the down arrow farthest left (next to the >) lists Previous locations, the 2nd arrow lists My Computer and the Desktop folders; the 3rd arrow lists the folders in the drive i am in; sometimes a 4th arrow lists the sub folder of the folder i am in; the 5th arrow lists previous locations, including the Internet ones. To go immediately up to the next folder, i would have to click the third arrow, find the folder i want, and click on it, but if i want to go up higher than that drive means the first. All such options are useful, but just clicking on the up arrow is faster and more institutive.
You can use the navigation pane for navigating, but this means an even wider window, and as Vista does not always remember Windows sizes after rebooting (remember each.. is checked), i prefer going without it.
Of course, if all i had was one partition on one drive, rather than 4 or more, or had little need to often navigate, then the speed of the up button may not be so desired, but it's no big deal anyway.