Setting _JAVA_OPTIONS='-DsocksProxyHost=127.0.0.1 -DsocksProxyPort=9999' in my environment before running Minecraft used to work to allow me to tunnel my traffic through an SSH-based socks tunnel to a personal server I run behind a NAT and firewall. This worked for every version I've tried up to and including 1.6.4.

After upgrading to 1.7.2, when I visit the multiplayer server list page, all my servers suddenly show up as "Can't connect to server".

I'm sure it's not an issue with the tunnel or with my server, since if I roll back to the 1.6.4 client (same launcher and environment) and use the same tunnel, the same server shows up in the server list as connected but with the expected "Client out of date" message.

I'm also sure it's not my java settings, since reading the log when running the 1.7.2 client still has the same line I'm used to seeing in my 1.6.4 client as it starts up:
[11:59:30 INFO]: Client> Picked up _JAVA_OPTIONS: -DsocksProxyHost=127.0.0.1 -DsocksProxyPort=9999

I've also run the same scenario back through all the post-1.6.4 snapshots available to me in the launcher, and here are my results:
1.6.4 -> "Client out of date" message
13w38c -> "Client out of date" message
13w39b -> "Client out of date" message
13w41a -> "Can't connect to server"
13w41b -> "Can't connect to server"
13w42b -> "Can't connect to server"
13w43a -> "Can't connect to server"
1.7 -> "Can't connect to server"
1.7.1 -> "Can't connect to server"
1.7.2 -> "Can't connect to server"