> take Google for instance (search and indexing), knowledge management systems (Wiki and other techniques) - these are all extensions of our brains.

I agree. But these two examples are different in a way that is important to me: my personal wiki is under my control; Google is not. Therefore, when I find important things in Google, I sometimes still take care to rewrite them into my wiki, using my own words.

Using the wiki feels like extending my brain. Using Google feels more like outsourcing it.