I too am having issues with my WiFi, I can't connect to anything for more than a few minutes. This is with my two WiFi networks at home and my WiFi network at work.
All three networks worked fine on my Cyanogenmod Droid X that I had prior to getting this phone.
At home, where it is an option, I even tried a non-DHCP, Static connection, and still no go.
I have tried combinations of all the Advanced settings, and currently I have "Sleep" set to Always on, "Optimization" off, "Best" On, and have tried forcing to both 5ghz and 2.4ghz.
Once I connect and get kicked off, the only way to reconnect, for the brief period of time I am connected, is to turn off WiFi and then to turn it back on. which buys me another few minutes of connectivity.
Quite a pain, thankfully I have grandfathered unlimited plan, but I still feel like this should not be happening...
I read about this being an issue with other HTC phones, and things like wiping the cache through the recovery menu (some even so far as to wipe the entire phone) got things to work. I've only once been able to get through the recovery menu into the Wipe Cache menu, which is another annoyance only partially related to this topic.
Regardless, the one wipe I attempted did not do me anything.