[Nexus S Q&A, Help & Troubleshooting] csdibiase@gmail.com:
Been tinkering more with this in my caffiene fulled late nights and I noticed a bit of a difference.

Before tethering, while the phone is working normally, getprop | net. returns the following spew:

[gsm.network.type]: [HSDPA:9]
[init.svc.netd]: [running]
[net.bt.name]: [Android]
[net.change]: [net.dnschange]
[net.dns1.137]: [172.16.145.103]
[net.dns1]: [172.16.145.103]
[net.dns2.137]: [172.16.145.103]
[net.dns2]: [172.16.145.103]
[net.dnschange]: [12]
[net.hostname]: [android-4d286c959aef935]
[net.qtaguid_enabled]: [1]
[net.rmnet0.dns1]: [172.16.145.103]
[net.rmnet0.dns2]: [172.16.145.103]
[net.rmnet0.gw]: [10.189.126.1]
[net.tcp.buffersize.default]: [4096,87380,110208,4096,16384,110208]
[net.tcp.buffersize.edge]: [4093,26280,35040,4096,16384,35040]
[net.tcp.buffersize.gprs]: [4092,8760,11680,4096,8760,11680]
[net.tcp.buffersize.hspa]: [4094,87380,262144,4096,16384,262144]
[net.tcp.buffersize.lte]: [524288,1048576,2097152,262144,524288,1048576]
[net.tcp.buffersize.umts]: [4094,87380,110208,4096,16384,110208]
[net.tcp.buffersize.wifi]: [524288,1048576,2097152,262144,524288,1048576]
[net.wlan0.dns1]: [49.0.0.0]
[net.wlan0.dns2]: []

With tethering enabled it looks like

[gsm.network.type]: [UMTS:3]
[init.svc.netd]: [running]
[net.bt.name]: [Android]
[net.change]: [net.rmnet0.gw]
[net.dns1]: [172.17.8.1]
[net.dns2]: []
[net.dnschange]: [10]
[net.hostname]: [android-4d286c959aef935]
[net.qtaguid_enabled]: [1]
[net.rmnet0.dns1]: []
[net.rmnet0.dns2]: []
[net.rmnet0.gw]: []
[net.tcp.buffersize.default]: [4096,87380,110208,4096,16384,110208]
[net.tcp.buffersize.edge]: [4093,26280,35040,4096,16384,35040]
[net.tcp.buffersize.gprs]: [4092,8760,11680,4096,8760,11680]
[net.tcp.buffersize.hspa]: [4094,87380,262144,4096,16384,262144]
[net.tcp.buffersize.lte]: [524288,1048576,2097152,262144,524288,1048576]
[net.tcp.buffersize.umts]: [4094,87380,110208,4096,16384,110208]
[net.tcp.buffersize.wifi]: [524288,1048576,2097152,262144,524288,1048576]
[net.wlan0.dns1]: [49.0.0.0]
[net.wlan0.dns2]: []

and after it's more or less the same

[gsm.network.type]: [UMTS:3]
[init.svc.netd]: [running]
[net.bt.name]: [Android]
[net.change]: [net.dnschange]
[net.dns1.137]: []
[net.dns1]: [172.16.145.103]
[net.dns2.137]: []
[net.dns2]: [172.16.145.103]
[net.dnschange]: [14]
[net.hostname]: [android-4d286c959aef935]
[net.qtaguid_enabled]: [1]
[net.rmnet0.dns1]: []
[net.rmnet0.dns2]: []
[net.rmnet0.gw]: []
[net.tcp.buffersize.default]: [4096,87380,110208,4096,16384,110208]
[net.tcp.buffersize.edge]: [4093,26280,35040,4096,16384,35040]
[net.tcp.buffersize.gprs]: [4092,8760,11680,4096,8760,11680]
[net.tcp.buffersize.hspa]: [4094,87380,262144,4096,16384,262144]
[net.tcp.buffersize.lte]: [524288,1048576,2097152,262144,524288,1048576]
[net.tcp.buffersize.umts]: [4094,87380,110208,4096,16384,110208]
[net.tcp.buffersize.wifi]: [524288,1048576,2097152,262144,524288,1048576]
[net.wlan0.dns1]: [49.0.0.0]
[net.wlan0.dns2]: []

By toggling mobile data on and off it goes back to

[gsm.network.type]: [UMTS:3]
[init.svc.netd]: [running]
[net.bt.name]: [Android]
[net.change]: [net.rmnet0.gw]
[net.dns1.137]: []
[net.dns1]: [172.16.145.103]
[net.dns2.137]: []
[net.dns2]: [172.16.145.103]
[net.dnschange]: [14]
[net.hostname]: [android-4d286c959aef935]
[net.qtaguid_enabled]: [1]
[net.rmnet0.dns1]: [172.16.145.103]
[net.rmnet0.dns2]: [172.16.145.103]
[net.rmnet0.gw]: [10.82.223.1]
[net.tcp.buffersize.default]: [4096,87380,110208,4096,16384,110208]
[net.tcp.buffersize.edge]: [4093,26280,35040,4096,16384,35040]
[net.tcp.buffersize.gprs]: [4092,8760,11680,4096,8760,11680]
[net.tcp.buffersize.hspa]: [4094,87380,262144,4096,16384,262144]
[net.tcp.buffersize.lte]: [524288,1048576,2097152,262144,524288,1048576]
[net.tcp.buffersize.umts]: [4094,87380,110208,4096,16384,110208]
[net.tcp.buffersize.wifi]: [524288,1048576,2097152,262144,524288,1048576]
[net.wlan0.dns1]: [49.0.0.0]
[net.wlan0.dns2]: []

Is there something just funky about my config or is this an android bug with tethering?