Found this @ XBMC forum

ATV2 WIFI Fixed!
Good news here folks!
I’m reposting from Twitter:

On Wednesday 16th February 2011, @nitoTV said:

the wifi fix is live!! thanks @saurik and @DHowett for major contributions to squelching the problem! it was an SSH issue and saurik has updated openssh to 5.8p1-9. grab openssh from the top of the nitoTV featured list and reboot and your wifi woes /should/ be history!!!