Hi PapaNew,
1. D+ stands for how many more democrats (as a percentage) will vote than Republicans
For example, on election day, out of a total of 100 voters, you had 40 Democrats, 35 Republicans and 25 Independents then you had a D+5 turnout.
So, in 2008 Democrats turned out in great numbers and were D+8. We are all (here on FR) hoping that this year it is D+1 or less.
2. Regarding “reliable” prognosis, take Rasmussen as your guide. He right now has Governor on a course to win (within the Margin of Error, ofcourse ;-))
Thanks SE and may God continue to have mercy and grace on our beloved country.