I was seeing a number of errors in the mediaplayer compilation section. Complaints about Phonon/Media and the like. Don't know why, presumably something's broken in how ubuntu installs them in the first place.

This is what it took to get ktorrent to compile in the latest ubuntu 10.4.

sudo apt-get install --reinstall phonon libqt4-phonon libqt4-phonon-dev libphonon-dev