At the risk of turning Waxy into a Jonathan Coulton fan site, he performed a short set at the Valve Software’s Steam Party capped by a finale of “Still Alive” performed on Rock Band, backed by the Harmonix developers on guitar and drums.
I’m pretty sure this is the only published photo of their final score, a 5-star performance:
And yes, Coulton sang his own song on “Easy.” (Afterwards, he said the Harmonix guys lowered the difficulty because thought the crowd noise would mess it up.)
Shortly after the set, I saw a tipsy geek hop on stage to copy the unreleased song from the Xbox 360 with a USB key before a Harmonix team member tackled him. I discovered he wrote up the story this morning, which was a fun read.