I successfully bid on and and received upgrades for both my outbound and return legs of my trip from IAD-AUH.
March 3, 2014: IAD-AUH EY130
Bid $800 for upgrade from Pearl Business to Diamond first and won.
*Received email from Etihad on March 1, 2014 that my offer was accepted and that I had been upgraded from Pearl Business to Diamond First
March 12, 2014: AUH-IAD EY131
Bid $700 for upgrade from Pearl Business to Diamond first and won.
*Received email from Etihad on March 10, 2014 that my offer was accepted and that I had been upgraded from Pearl Business to Diamond First
I hope that helps.