Does Youtube app playback not work with wifi? On an HTC Evo with Sprint, when trying to playback a video, the Youtube app regularly (always?) reports it can't play a video when I'm connected to a reliable wifi network.  If I immediately turn off wifi and use only the Sprint network, it works fine.

Is this really the case?  If so, why?
After some experimentation: the EVO on Sprint can playback YouTube over WiFi.  The problem is likely some domain being blocked by the hosting WiFi network which is necessary for the YouTube app.