In the first of a series of posts, Rachmi Sinha explores the progress made in the realm of collaborative filtering,  recommendation systems and the implications of tagging:
"So are tags and collaborative filtering a marriage made in heaven? It's a promising approach, but there are challenges in making it work - some challenges inherent to tagging, and other challenges inherent to collaborative filtering. The question is - does the combination of tagging and collaborative filtering solve those challenges, or only make it worse? I don't have any magic bullets (if you were looking for an easy answer, stop reading now.) Instead I have a bunch of observations in no particular order."
I'm looking forward to her further thoughts on this.

(btw, she has a fascinating bio)