I don't know if this has anything to do with it, but I've been doing some investigation, and it looks to me like one of these files might be corrupted:
$ sudo /usr/sbin/slapt-get --filelist kdenetwork-4.3.5-i486-1 |grep kopete_yahoo
And I'm guessing it would the kopete_yahoo.so since that's the only one that could be a library or plugin file. I'm wondering if replacing that file with an older one would make a difference.
What do you guys think? I am going to at least compare this list with a list of files in an older package.
Okay, I installed kdenetwork-4.2.4-i486-2.txz from the Slackware mirror, and it now works perfectly... Only thing I can think is that some file got corrupted somewhere... I will try tomorrow to get upgraded tomorrow and have it work. Not sure, though. If this is a distribution problem, who should be alerted? I already posted a bug report on bugs.kde.org just in case...