after logging into kde, kactivitymanagerd uses 100% cpu until I kill it. not sure what is causing it

I looked on bugs.kde.org and Google'ed and saw nothing regarding kactivitymanagerd and cpu usage, assuming this is a new issue is there anything that recently change on your system or config? Is there excessive memory usage in the process?

do you have a large number of activities running?
does a new/diff user have the same issue?

you can try clearing the kde cache when your session is not running /var/tmp/kdecache-<username>
and within KDE running: kbuildsycoca4 --noincremental

Also, do you have Nepomuk enabled?