I'm at the University of Texas, where we have a WPA/WPA2 enterprise wifi network. Much of the time it works great. Other times, it's tricky to connect and stay connected.
I can actually force it to connect long enough to load a webpage or two if I go into System Preferences > Network > Wi-Fi. In the bottom half of the window it's got
802.1X: Wi-Fi (restricted.utexas.edu) next to a Connect button.
If I push connect, it says:
Authenticated via TTLS Connect Time: 00:00:00
and then starts counting up. When it hits about 5 seconds, I find that I can load webpages. The Wi-Fi indicator, however, seems to think it's not connected (won't show the solid connection indicator, just the trying-to-connect animation), and after about 52 seconds, it seems to give up and decide it's time to try again -- which actually disconnects me.
Even after about two years of this I haven't found a consistent way of handling the problem other than rebooting the Macbook altogether. I find it'll connect eventually even if I don't. Turning Wi-Fi off and on may or may not help, but that may be my imagination.
I'd love to find a solution to this problem that doesn't involve rebooting, for obvious reasons. It's just not sustainable, because sometimes the computer will idle-to-suspend and then lose the connection again, which requires another reboot.
I'm using OS X version 10.8.4.