Coldplay officially responded to Joe Satriani's allegations.  The following was posted to their website today:

"With the greatest possible respect to Joe Satriani, we have now unfortunately found it necessary to respond publicly to his allegations. If there are any similarities between our two pieces of music, they are entirely coincidental, and just as surprising to us as to him. Joe Satriani is a great musician, but he did not write or have any influence on the song Viva La Vida. We respectfully ask him to accept our assurances of this and wish him well with all future endeavours."