I can just see how a Romney-Senate-House Trifecta will be reported as a call for Power Sharing by the American people by the press..
Then just a few months later Jim Jeffords jumped parties and the Democrats had 51 so they kept to the power sharing agreement, right? Right? Uh, no. They went all in with Bush bashing Tom Daschle/Harry Reid/Nancy Pelosi attack machines 24x7 and worked overtime to kill everything the GOP tried to do.
The RINO leadership is on triple secret probation with me already. If they throw away the gains of the 2010 and (with your scenario) 2012 elections by agreeing to share power with the democrats it will be the last straw for me. At that point, I might just finally go third party.