Same here :-(
Same issue here after Absinthe jailbreak on 5.1.1 on AT&T iPhone 4S. MyWi worked fine on 5.0.1.
Tried remove-reinstall, changed channel, removed security so it's just open, changed SSID name but no luck.
The client gets an IP but no traffic flows to/from the 3G connection -- up/down indicator also shows 0 bytes transferred.
I tried it from my "new iPad" client, a Windows 8 laptop, and an iPod and get the same results. Same result on both USB and Bluetooth tethering as well.
Also, once I jailbroke my new iPad, I installed and tried the "on demand" feature and as expected, same results -- it connects but I don't get any data.
Let's hope it gets updated!