There will be a slight variance between states, plus the difference in each state's non-Latino results will make a difference. Nationally though, I'd say around 40%, give or take a couple of points.
Yeah I have heard in the past thats what the GOP targets to get around 40% of the Hispanic Vote. They did get 38% of the Hispanic Vote in the 2010 cycle. It will be hard for the GOP to get 40% this time around because of Romney's extreme right hard line on immigration reform. Add in the Arizona Immigration Law too and Obama declaring last summer I think that he won't deport non-criminal illegal immigrants.
I think Romney will get around what McCain got of the Hispanic Vote in 2008(31%.)