"Knowledge is of two kinds: we know a subject ourselves, or we know where we can find information upon it."Samuel Johnson had the idea of transactive memory down before Wegner, Giuliano, and Hertel formally brought it to the table in 1985.
What it acknowledges is that there's memory in our heads, and memory that's elsewhere, usually other people's heads. Transactive memory is the smearing of a reality to a number of different minds to lighten the load on one.
Swap out the 'other people' in this arrangement and swap in the Internet. Feel familiar? As Clive Thompson said in Wired, "Almost without noticing it, we’ve outsourced important peripheral brain functions to the silicon around us."
Just as the nature of transactive memory in relationships or groups is only conspicuous by someone's absence, so it is when we are away from the Internet. Our memories are now neuronal and digital. Sounds rather cyborgish, doesn't it? But a hefty chunk of my memory - names, numbers, dates, addresses, quotations - are all outsourced.
Wegner and his mates should broaden their research to see what's going on with transactive digital memories.