I am also having this problem, but think I may have found a workaround.
I was noticing extreme amounts of packet loss. I could not get through even a 10 minute YouTube video without it dropping out after 2-3 minutes. Streaming from iTunes was even worse, usually only lasting about 30 seconds. I pinged my Apple TV from my laptop and it was dropping the occasional packet (perhaps once every 50 pings), but every now and again it would completely drop off the network for about 30 seconds or so -- which caused whatever I was watching to stop and boot me back to the home screen. I played around with my WiFi settings (changing channels etc), and after about an hour of trying absolutely everything I could think of, I reconfigured my security settings to use WPA2 + AES instead of WPA2 + TKIP. As soon I enabled AES only, my Apple TV started working flawlessly. Coincidence? Who knows, but I then watched two ABC iView episodes via AirPlay and watched a 15 minute video podcast from my iTunes library all with absolutely no problems.
My Apple TV was only purchased a few days ago, but had worked fine up until I installed the update yesterday. I'm now considering just biting the bullet and running an Ethernet cable to it.
When I get home tonight, I'll no doubt want to watch some TV again so I'll report back if it seems to be solid again.
tl;dr - Try disabling TKIP and only use AES. This worked for me, was working fine before the update.