I wanted to toss in a few words about setting up wifi even though I'm a few pages late, because I've found that it's not hard to grasp once it's been explained.
The main reason to get wifi is because it's wireless. That sounds pretty self-explanatory, but for people who've never heard of it, it does need to be said. The wifi device sets up a field around itself that allows devices to communicate with each other and the outside world without running wires all over the house. We got a wifi point because we got several portable devices (a laptop and iPod) and the wifi allows visitors to connect to our network without plugging in. But now we use it for quite a few stationary devices as well, like the Wii and one of the computers. Setting it up to work at all is as simple as plugging it in, connecting it to your existing Internet connection, and giving it a name. That's very insecure, but it'll work with just that much.
Securing it is a good idea because it's a field. That means that when devices connect to it, they broadcast information to the wifi device and the wifi broadcasts information back to the devices. The devices don't broadcast in a line, so anyone in range can "listen in" on the conversation, and that can mean that someone in a nearby house can "see" what user name and password you entered when you logged into your bank account web site. Therefore, wifi devices come with encryption. This feature causes the devices to scramble the signals they send and unscramble the information they receive. If someone listens in but doesn't have the correct password, all they'll "see" is jibberish, so it's safer to send sensitive information around with encrypted wifi. Every wifi device provides an interface (a built-in mini web site on the device itself) that lets you set up encryption. artk2002 mentioned MAC address filtering as well. Every device that connects to the Internet (computers, TVs, iPods, phones, whatever) has a unique address that's built into the device itself, called a MAC address. You can set up your wireless point to allow only approved MAC addresses to connect, so anyone in range who tries to connect but doesn't have an approved MAC address would be refused even if they guessed your password. This adds an extra layer of security on top of encryption by keeping unauthorized people off your wifi entirely.
So, the short story is that it's easy to set up and a bit challenging to secure, but it's not anything that the average person would be unable to do.