Yes, greatly slowed and that's troubling considering all the cash that American corporations are sitting on right now. That said, the indicators are still vastly different from what we saw in the last 20-30 years even of the Soviet economy, so the main point was that soviet bureaucracy worked hard to make up for a structural decline in productivity, while American bureaucracy seems to just grow with time despite productivity growth.
The slower rate of TFP growth occurred before the concentration of wealth, not after. So it's hard to argue that it is related at all to the phenomenon under discussion.
Why can't it be related? I see plenty of ways for the TFP to be related to the concentration.
For example, here's one model which nicely matches the TFP lack of growth and subsequent wealth concentration: 'the wealthy 1% demands a fixed additional sum per year (due to some sort of hedonic treadmill or cultural imperative - relative status seeking perhaps); while TFP growth exceeds this fixed sum, we will see the additional wealth distributed to the other 99% through wages etc. Once TFP falls below this sum, all TFP gains now go to the 1% and everyone else stagnates.'
A growth which has massively slowed. That it hasn't actually been outright negative is cold comfort.
Look at total factor productivity in the US: http://macromarketmusings.blogspot.com/2011/02/great-stagnat... (Notice all the supporting citations to other productivity measures in the comments.)