Same here. I still don't have a good solution to horizontal scrolling (shift doesn't work in Excel).
It's great for spreadsheets. I even use the Macbook trackpad for 3D CAD. I used to use a spaceball and mouse, but the trackpad plus modifier keys is more convenient because it keeps the hands to the keyboard.
I know many people that use a mouse and Magic Trackpad and fluidly switch between them depending on the task. I did exactly that for about a year—before eventually ditching the mouse altogether.