re: I'm pro-nuclear and think RTGs are safe but ....
I understood that the delay in MSL from '07 to '09 was to allow a switch from solar to RTG power. It was felt that the delay was balanced out by the advantages of RTG power, and it constitutes the sole correct decision of the Bush Administration. I exaggerate slightly, maybe.
As for MSL getting cancelled, I think it's a slight risk as budget deficits come home to roost and the scientifically-marginal JIMO program sucks up funding. I think MSL will squeeze through the bottleneck though - it's all the big missions after '09 that will have their oxygen cut off. Goodbye, Mars sample return.