Same issue here. Tonnes of people posting about this today.
FTR, I'm testing on a Q6600 @ 3GHz per, 4GB RAM, blah blah blah.
I notice that as of 2.0.1, even decoding a 128kbps mp3 is chewing a full core by itself.
As noted by everyone else, rolling back to 1.1.9 solves the issue.