As is being reported around the net 3rd party ICQ clients Pidgin and Kopete are are stuck ICQ-less until patches get merged into the systems. Pidgin is affected in the Linux and Windows world, fixes are available but to my knowledge these are only temporary or proposed and not anything official.
Ubuntu temp fixes: https://bugs.launchpad.net/ubuntu/+source/pidgin/+bug/244591
Windows temp fixes: http://developer.pidgin.im/attachment/ticket/6220/liboscar.zip
You have to love unannounced protocol changes! :)