If the link between your WiFi laptop and your Access Point (or Wireless Router) is setup using the highest level of WiFi encryption, then your browsing is just as secure as it was when you were hard-wired into your router: data from laptop->AP are secure, date from Router->Public internet are not secure (same as being hardwired before).

What you do gain, by using something like anonymizer.com, is in making your data packets be secure between your access to the public internet and wherever Anonymizer's secure server is located. However, the data you send still has to go from Anonymizer's server to the site you are browsing, say anonymizer.com->microsoft.com.

There are other ways to accomplish this, such as use client software you install on your windows OS, such as GhostSurf Pro, Steganos, and Proxomitron (freeware, I think), and there are others. There's also an active subculture of people who configure proxy servers to maintain some level or security between their PCs, and their connection to the public internet.

Hope this helps, ... anyone with experiences?