...and I'm back once again. The pinging results in Terminal aren't guaranteed to keep my connection from getting hosed, unfortunately.
I had two different terminal sessions pinging two different machines at the same time and it would still drop. What was interesting was that one of the sessions I didn't pipe to /dev/null so I could see that the pings would just go off into nowhere for stretches at a time, about 1-2 seconds and then restablish for a second, cycling through that until it ultimately failed.
This is a 2013 MacBook Air with i7/8GB/512, running with bluetooth off and powernap off. SMC and PRAM have been reset. A new user account was created as well, and updated to 10.9.2 beta 3 (13c44).
Changing to a static IP does not seem to help. After losing internet access, the airport symbol is still on and the system still believes it is connected. Disconnecting and reconnecting appear to work but in reality no internet connection functions. Reconnecting and trying the internet will sometimes show the airport logo to disconnect with an exclamation mark, but a reconnection attempt appears to succeed without any working network.
The only solution is to wait around 5-10 minutes and try again, or shut down the machine and reboot it to try again.
The connection that I know is problematic is a 802.11 b/g station running DD-WRT with a WPA password.
Open hotspots and Apple wifi products (Airport Extreme AC) don't seem to be affected.
I was going to head to the Apple store to get a 13" Macbook Pro Retina as a replacement but it appears those are affected as well? Makes me wish I didn't give away my MBA 2011.