"surpass relational databases in popularity by 2011"

Are you really sure about that? AFAIK the use case for key-value stores isn't one that a lot of people are going to suffer (seriously high-volume).

I think there was a lot of excitement about XML databases around that time, because they would let you store more complex structures in the DB, not less complex (like key-value). Somehow XML did not take off, not sure why.