Ppl seems to hate successful projects. Mongo is probably the most successful noSQL db out there (not going in a war on its merits and flaws) and now people hate it. I wonder how long will take for us to start reading stories on "Why I hate Riak"
Meh. Single threaded map reduce and very hungry disk usage. Mongo isn't the silver bullet a lot of supporters sometimes project it as (not saying you are).
Also, he actually linked 2 articles, I'd never seen the first one so it may very well be a hoax or whatever. But the 2nd one has made it's rounds a few times and has stood up (IMO) to scrutiny.