A wise thing to do but many wirless networks appear open access but does not all ways means you can connect.
I know a mate leaves his open and restricts access to the router and everything behind in other ways.
But if you see an open connection dont click on it with out considering the possiblle implications to your pc, many are either due to people deciding to keep it open for their own reasons or dont know better. Possibly if you connect to those your get internet connection.
But some are like that as a form of trap, unlikely in a residnetial area but i am aware of cases in towns and cities. Many will allow you to connect to the internet. But remeber all your data passes to and from them. Also what is being uploaded on to your pc?