The "Flap" on the top can be opened to reveal 4 GCN controller ports and 2 GCN memory card ports.
The Wii has a sort of WaveBird reciever built into it (notice that the top is flat, while the GCN is curved? Wavebird revievers wouldn't fit).
The "Flap" on the front contains 2 ports of some sort (Flash memory, or something like that), and the Synchronize button (for controllers, read further).
The wiimote knows where it is pointing because of a sensor bar you play over or under your TV. There is a calibration function that prompts you to point at 2 points on the screen. It is not a light gun...
The Wii controllers know which console in a room full of consoles they belong to because of a Syncronize button placed both on the Wii and the Wiimote (under the battery thing).
There was also something about the pointer in the Wiimote sensing a 1024*768 resolution picture, which led to rumors about a camera being contained in the Wiimote. It could just be used for knowing where it is, etc., though.
Oh yeah, and the Wiimote (or rather, the sensor bar) can get disturbances from strong light sources and stuff of that sort, so I wouldn't set it next to an open window with the sun pouring down on it.