No, there is no inherent "data privacy" in 802.11 wireless networks.
A WiFi connection can, but must not be encrypted. That's not to say it shouldn't be if you care about your data. A simple connection is always unencrypted at the data link level, and packets travelling over the air can be easily sniffed by others within reach of the base station or your WiFi adapter. Plain HTTP traffic is really easy to analyze. You don't need to be a hacker to be able to do that.
A simple encryption method that has originally been defined in the IEEE 802.11 standard is WEP (Wireless Equivalent Privacy), but it has been found to be a very weak encryption technology since its key scheduling algorithm could be easily hacked.
So, given enough time, anybody could crack WEP encryption and therefore sniff packets as if they were unencrypted.
Finally, WPA and WPA2 (Wi-Fi Protected Access) offer a very robust encryption that is likely to protect all data travelling over the air—given that a strong enough password is used. Even if your data is HTTP, another user won't be able to decipher captured packets. Some attacks have been found (involving pre-shared keys, see the link above for more), but they're quite irrelevant these days.
Still, make sure that your password is strong enough, otherwise the only limiting factor for an attacker is time.
There exist network level attacks, such as ARP spoofing and rogue DHCP, that allow other users on the network to convince your computer to route traffic through their device as a proxy. This lets them inspect traffic, even intercepting SSL connections. These work regardless of wireless encryption, and are difficult to defend against on public networks. See this IT Security question