I'm with Szalkow all the way.
As far as speed's concerned, the reading speed of my USB2 is noticeably faster than a retail disc, let alone a backup disc.
As far as simplicity is concerned, you can get things a easier than disc loading as well. Loadstructor's one way. And after some fiddling with priiloader and usCFG, starting my wii is now literally 2 clicks away from starting my favorite games. And that includes 1 click to synchronize the wiimote.
NOTE: the latter isn't aimed at discs vs usb (you can get it to start a disc to load in 2 clicks in the same way), but to the argument that usb loaders have to "start another program" first...which simply isn't true (why the heck would we want to load the system menu in the first place?).