I'll say this. The conditions are right for Boxer to go down. She's a dreadful candidate. There's a strong anti-incumbent sentiment in this country. There's an even stronger anti Obama and anti progressive sentiment. Republicans and conservatives will likely be more motivated for turnout than liberals and Democrats.
So, who knows. I really hope she loses, but it's hard to say right now. Boxer's poll numbers are low enough that it's possible. It'll be easier to get a feel for this race after the Republican primary.
I'd say there are at least eight other Senate races that will be easier for the Republicans to gain seats though (Indiana, Delaware, Pennsylvania, Illinois, Colorado, Nevada, Arkansas and North Dakota). If the Republicans win Boxer's seat, then they'll likely have won the others, which would mean at least 50 seats for the Republicans. The Democratic seats in Washington and Wisconsin might also be "in play" depending on the Republican candidate that enters these races.