Is the CPU on the iBook upgradable? How is it mounted?

Depending on the model, the processor in the iBook models is either soldered to the motherboard or soldered to a daughtercard that also contains the ROM. It is not feasible to upgrade the processor.

Does the iBook have expansion slots or bays? What type?

No. None of the iBook models have expansion slots or bays of any type.

Do the iBook models support VGA or DVI out? Do the iBook models support ADC (Apple Display Connector) displays?

No iBook models support DVI (Digital Video Interface) or ADC (Apple Display Connector). Some iBook systems support mini-VGA, others VGA via an "A/V port", and some not at all.

This information is provided on the particular specs page for each model, but also is provided below in a handy chart for your convenience:

iBook	Ext. Display Connection
iBook G3/300 (Original/Clamshell)	None
iBook G3/366 SE (Original/Clamshell)	None
iBook G3/366 (Firewire/Clamshell)	None†
iBook G3/466 SE (Firewire/Clamshell)	None†
iBook G3/500 (Dual USB - Tr)	1* (VGA)
iBook G3/500 (Late 2001 - Tr)	1* (VGA)
iBook G3/600 (Late 2001 - Tr)	1* (VGA)
iBook G3/600 14-Inch (Early 2002 - Tr)	1* (VGA)
iBook G3/600 (16 VRAM - Tr)	1 (Mini-VGA)
iBook G3/700 (16 VRAM - Tr)	1 (Mini-VGA)
iBook G3/700 14-Inch (16 VRAM - Tr)	1 (Mini-VGA)
iBook G3/700 (16 VRAM - Op)	1 (Mini-VGA)
iBook G3/800 (32 VRAM - Tr)	1 (Mini-VGA)
iBook G3/800 14-Inch (32 VRAM - Tr)	1 (Mini-VGA)
iBook G3/800 (Early 2003 - Op)	1 (Mini-VGA)
iBook G3/900 (Early 2003 - Op)	1 (Mini-VGA)
iBook G3/900 14-Inch (Early 2003 - Op)	1 (Mini-VGA)
iBook G4/800 12-Inch (Original - Op)	1 (Mini-VGA)
iBook G4/933 14-Inch (Original - Op)	1 (Mini-VGA)
iBook G4/1.0 14-Inch (Original - Op)	1 (Mini-VGA)
iBook G4/1.0 12-Inch (Early 2004 - Op)	1 (Mini-VGA)
iBook G4/1.0 14-Inch (Early 2004 - Op)	1 (Mini-VGA)
iBook G4/1.2 14-Inch (Early 2004 - Op)	1 (Mini-VGA)
iBook G4/1.2 12-Inch (Late 2004 - Op)	1 (Mini-VGA)
iBook G4/1.33 14-Inch (Late 2004 - Op)	1 (Mini-VGA)
iBook G4/1.33 12-Inch (Mid-2005 - Op)	1 (Mini-VGA)
iBook G4/1.42 14-Inch (Mid-2005 - Op)	1 (Mini-VGA)

†These models can mirror the contents of the internal display on a television or projector via composite video out using the A/V port. Neither can support a second monitor.

*These models support VGA via the A/V port.

Also see: What kind of video processor is provided by the iBook models? Which models can support an external display? What is the maximum resolution supported?

What is the "Sudden Motion Sensor"? How does it work?

The Apple "Sudden Motion Sensor," provided by the last iBook models -- the iBook G4/1.33 12-Inch (Mid-2005 - Op) and G4/1.42 14-Inch (Mid-2005 - Op) -- is a tri-axis accelerometer that detects sudden changes in "position and accelerated movement".

In the event that one of these systems are dropped or fall off a desk, the Sudden Motion Sensor reacts by stopping the movement of the hard drive heads so that the disk platters won't be scratched when the notebook impacts the floor. This makes it less likely that the hard drive will be damaged.

For more information on the Sudden Motion Sensor, please refer to "About the Sudden Motion Sensor" and "Sudden Motion Sensor: Advanced Tips" from the Apple Support Site.

What is the "Scrolling Trackpad"? How do you use it?

The "Scrolling Trackpad," provided by the last iBook models -- the iBook G4/1.33 12-Inch (Mid-2005 - Op) and G4/1.42 14-Inch (Mid-2005 - Op) -- is a trackpad that allows one to scroll or pan by touching the trackpad with two fingers instead of one. This is particularly convenient for reading content quickly.