Whenever you use your notebook computer to connect to a public or private wireless network, it adds an entry for that network in to the 'Preferred Network' list. This list is meant to remember your network settings when you move from wireless network to network. The problem is that if you move between a lot of different wireless networks this list can get really filled up with a lot of junk that can slowdown your network connection time.
Another problem that happens often is that you can find yourself constantly being connected to a wireless network that you don't want to be connected to. This problem is caused by the fact that the entry for the wireless network that you don't want to be connected has a higher order of preference then your preferred network.
To fix both of these problems: