If you have a laptop and use any of the thousands of WiFi hotspots that are available, you could be opening yourself up to a security risk that you might not be aware of. You have no guarantee that the WiFi hotspot network's DNS information has not been compromised.
For those who don't know what DNS is, its a service that translates domain names (i.e.: BLOGGER.COM) into the IP address (i.e.: 220.127.116.11) that is used for directing your browser to the right destination. This is only a real quick introduction to the technology if you want more information, check out this article from Wikipedia.
It's possible for someone to point a wireless router's DNS anywhere they want. For example, someone can changed the DNS servers to ones will take you rogue web sites that look like the legitimate one to steal your personal information. Note: This type of attack can be very difficult to detect.
By making a service such as OpenDNS (a free DNS service) your main DNS provider, you can help protect yourself while your roaming with your laptop. What you do, is leave your DHCP service running to get an IP address automatically assigned to you when you join a hotspot's network, but you can override the DNS information it wants to assign to you and use OpenDNS instead.
Here are the instructions you will need to setup your local computer, our home router. OpenDNS also offers many other features like parental controls, shortcuts and more.