On a Thinkpad X220 with a built-in microphone and speakers, a test with empathy and sofiasip reveals that echo cancellation does not work at all.
This is on Fedora 16 with the following packages:
echo cancellation is done using a pulseaudio plugin. Which version of PA were you using?
This is pulseaudio 0.9.23.
...and I'm an idiot for blindly assuming that the version of pulseaudio provided in Fedora was the latest :)