Alex has wrote a blog entry on the speed issue of LDA and released his fast LDA algorithm that performs on many computers. Here is the blog entry: http://blog.smola.org/post/6359713161/speeding-up-latent-dirichlet-allocation
In Purdue's MLSS 2011, I was lucky to attend his lectures on graphical models. I like his lectures. The only regret is that I really hope he could give more details on LDA and its variants; for example, giving a detailed development on a variant of LDA models. But I understand the time was limited. After all, the lectures serve for a seminar, not for a college class.