You use the zoom ring in conjunction with the buttons and switches to control most of the manual features. The Cam Func button is quite small and difficult to manipulate without looking, unfortunately.
The SD100 has a traditional zoom switch with a very nice, responsive feel that makes it easy to get a controlled zoom. The camcorder also has a switch to toggle between the EVF and the LCD, which is odd but nice; usually the camcorder automatically switches when you open the LCD.
The joystick's location makes it disorienting to use, and it's a bit too recessed, which makes it difficult to manipulate. Thankfully, you don't need to use it too much--unless you use face detection, night mode, telemacro, or other marginal shooting features.