I've [asked about this](http://metaoptimize.com/qa/questions/8076/does-not-centering-data-hurt-when-doing-pca) on MetaOptimize, and read quite a bit about PCA vs. LSA, and just about everyone seems to agree that when you don't center, you can't call the result PCA (and I'm not sure if the `explained_variance_` member still contains what its name indicates).