On NRO today, John J. Miller runs down the 2010 Senate races. It's very early, so these are about as accurate as using, say, the rings on a single tree in Siberia to predict global warming. But if you assume the toss-ups really are basically 50/50 propositions and that the leaning or likely retentions hold as Miller predicts, then the GOP picks up just one seat. (Eight toss-ups, five for Dem seats and three for GOP seats.) Of course, with the 60-40 Senate balance today, one seat is a big deal.
Here are the toss-ups: Colorado (Dem), Connecticut (Dem), Missouri (Rep), Nevada (Dem), New Hampshire (Rep), North Dakota (Dem), Ohio (Rep), Pennsylvania (Dem).