Do you ever plug in your wired network card while your Wi-Fi connection is still enabled? Here's how to see which network interface has priority, and how to change it if you want.
Over at the How-To Geek site (my home away from Lifehacker), we've written up a guide for how to tweak the default priority of each interface if you want to — for instance, if you wanted to make sure your Wi-Fi connection was the default even if you plugged in the wired connection, so that you wouldn't get disconnected when you switch. To view the current interface priority, you can use the netstat command, which will show the priority to the left of the interface list:
To tweak the interface priority settings for yourself, just head into Network Connections -> Properties -> TCP/IP Version 4 -> Advanced and change the default priority there — you'll probably need to make the same setting change for each card.
Hit the link for the full explanation and walkthrough. Note that you won't generally need to change these settings, but it's still good to know how to do so if you want to.