Quoting Patrick O'Callaghan <pocallaghan(a)gmail.com>:
Did you update to KDE 4.4? If so, check recent postings on the Fedora
KDE list. There are some problems with akonadi. See
https://admin.fedoraproject.org/mailman/listinfo/kde
FWIW, I'm still on F11 and it's been working great until this morning
when I noticed the system was acting like it was trying to get my
attention to update... so I used the SSH console I was in to start the
update and noticed a bunch of updates come through... *sigh* I wish
I'd known about the KDE4.4 problems... pisses me off that stuff that
should have been better tested was pushed out broken!