I think it's different this time. The pubbies gave GWB just about everything he wanted, and the independents cleaned their clocks in 2006 and 2008.
Remember when talk about renewing an "assault weapons" ban in 2009. IIRC, Reid and Pelosi said to forget about it, and 64 House rats sent a letter to Holder to the same effect. They campaigned on being pro Second Amendment.
The Tea Party Congress critters campaigned on being fiscally conservative most of all. IMHO, Romney will have to worry most about conservatives opposing him.
Let us hope they really do oppose him. If FR is any gauge, they're simply going to roll over when he shows them that nice big R on his sleeve.