Add me too. Can't connect to 5ghz at all, but 2.4ghz seems to work fine. 5ghz was working perfectly smooth on Maverics. I have an Asus AC66U here.
In my case seems to be a problem related with authentication. If I set the 5Ghz 802.11ac network on the AC66U to open it connects fine, same thing if I choose WPA personal instead of WPA2 personal. Sadly, it seems the rMBP will only do 80Mhz ac channels on WPA2 so if you choose any other option you are stuck at 486Mbps max.. annoying