So the impact of the restoration of capitalism is "not massive". Try going shopping without buying something that wasn't made in China.
Reasonable estimates conclude that the restoration of capitalism in the former Stalinist states increased the size of the world market by around 20%. The test of whether that is or is not "massive" is whether it has enabled profitability across the world to recover. And basically it has, profitability "the most important law in political economy" according to Karl Marx, is at its highest levels since the mid 1960s and there have been 15 successive quarters of 10+ profit growth in the USA. In the UK profits are even higher - the rate of return is at its highest level since 1963.
The reason Harman uses four year old statistics (when its just as easy to use the uptodate ones) is quite simply because his argument - that the world economy is in deeper crisis today than it was during the 1970s/80s - simply doesn't stand up based on the current data. It's a quite concious attempt to mislead the reader.
Are large sections of the world economy overinflated? Well it depends what you mean - since globalisation the world economy has become more stable notwithstanding the huge increase in speculation and financial flows. In fact price/earnings ratios on equitities have declined over the last three years, even as stock markets have risen, because profitability has risen even faster.
Certainly the collapse of the US housing market, probably worth around 0.25% of global GDP, did cause a slowing of the US economy in the third quarter of 06, but figures for the last quarter showed that this was not going to lead to a recession in the USA.
What's even more remarkable about Harman's piece is in spite of his economic catastrophism (what else can you call a theory which asserts that the world economy is stagnant at present) is his equivocation and uncertainty. Why doesn't he think the world's in a world revolutionary situation (never mind pre-revolutionary) if the world economy is in such dire straits?
It's a common feature of all the catastrophists - SWP, the Socialist Party - who predict an economic ressession - "this year" - Workers Power - etc. that rather than trying to assess the effect of the restoration of capitalism on the world economy, they simply want to deny it. Ultimately it shows they have no faith in the working class - its as if an admission capitalism was capable of recovery means that socialism's off the agenda - this is absolutely not the case of course, but is the flip side of their desperate and increasingly feeble attempts to deny reality. (John Rees does it as well in Imperialism and Resistance.)
Ultimately its the abandonment of Marxism as a science and personally I was never religious.