If you believe that only Open and WEP configurations are unsafe and do not provide inter user privacy, its high time to get yourself updated about a new security weakness as WPA TOO has also been found vulnerable. The weakness is inherited in the protocol due to a design choice made by the architects of the 802.11i standard.
Since a lot has been already said and written about it, so instead of writing it by myself, I would redirect you to some interesting and informative articles here.
The most recent article written on this topic can be read here.
A copy of the slide deck presented in the Defcon 18 can be found here.
WPA/WPA2 protocol allows users to establish a mutual trust relationship between Wi-Fi users and network which carry a transitive relationship due to use of a shared key. And hence WPA/WPA2 users end up establishing an unintentional trust relationship among each other. The trust relation is exploited by malicious Wi-Fi user to redirect legitimate users traffic and gain access to their private data.
The security risk is low in an enterprise network environment where most users are trusted insider though insider threats are increasing and act of spying has also gotton some attention, the risk becomes extremely high in WPA/WPA2 enabled public Wi-Fi hotspots. Such networks are also setup in conference. Security enabled Municipal Wi-Fi (Google-Secure) and Guest Wi-Fi networks are also gaining popularity.
In next blog post, I would share insight on some mitigation strategies discussed and proposed by community.