Here's two very interesting posts on ancient admixture / introgression between Homo sapience and ancestral Homos by Razib:
I'm still not completely convinced by the various studies showing evidence for this; many of them are heavily model based and there are just so many possible artifacts here. Speaking from experience. Still, it isn't that far fetched that the simple out of African model is too simple to be correct.
I had actually missed the PLoS ONE paper discussed in the second of the posts, but skimmed through it quickly today. It looks very interesting, but I want to get my head around the model used. Hopefully I can find time for that early next week.
I really look forward to reading the Neandertal paper and see what it has to say about geneflow between us and Neandertals. A few month ago, while I visited his group in Leipzig, Svante Pääbo actually promised to show me the draft, but it never happened. In Ohio in February I talked to one of the authors on the paper and he wouldn't reveal anything... I guess I just have to wait and can only hope that it won't be too long.
Update: See also John Hawks Population models and testing human origins