Network problems after Jailbreakme on iPhone
That happened to me too, and now my wifi doesn't work anymore so you should expect that. (not much an answer just a comment)

3 possible fixes you can try: (they did not work for me)

1) Reset network settings: Settings -> General -> Reset -> Reset Network Settings.
3) When connected to your network click more info (the little > icon) and check if DHCP is enabled.
2) The last thing Restore your device from Itunes or reset the device from Settings -> General -> Reset -> Reset All Settings.