Well, hopefully you have your network encrypted, which will keep out most freeloaders. Still, if you want to double-check, grab a program like Wireless Network Watcher that shows you every gadget connected to the network. Check it occasionally and make sure you're the only one connected. Click here for some more signs and what to do if your neighbor is sneaking through your network security.
The Internet is a great social networking tool. You can stay in touch with friends, find out who lives near you, share photos and talk about current events. Do you want to learn more about someone?