There has been a pretty lively debate on this topic over at Language Log. Geoff Pullum starts off with questioning the classification of languages into weak and strong FTR:

If English has future tense markers at all, it has at least a dozen of different ones; but simple use of the present tense is a very prominent way of referring to future time, so what do we make of that? For my part, I have no confidence at all that English is accurately described as "strong FTR". Nearly all traditional grammarians report English as having a tense system that includes a future tense, but that isn't really true; will is a modal auxiliary that has various other uses too. If the facts are shaky for English, how likely are they to be accurate on languages that have not been studied nearly so intensively?

I also worry that it is too easy to find correlations of this kind, and we don't have any idea just how easy until a concerted effort has been made to show that the spurious ones are not supportable. For example, if we took "has (vs. does not have) pharyngeal consonants", or "uses (vs. does not use) close front rounded vowels", would we find correlations there too? I have some colleagues here at the University of Edinburgh, within Simon Kirby's research group, who have run some informal experiments on the data Chen uses to see if dredging up spurious correlations of this kind is easy or hard, and so far they have found it jaw-droppingly easy. (I won't say any more, because I am in the weird position of writing unrefereed telegraphing of unrefereed and informal objections to an unrefereed and unpublished working paper, and it's all getting a bit too weird for me.)

Mark Liberman's post is worth reading in its entirety. He tries to argue that the fact cultural traits spread geographically in correlated ways means that we can not read too much into the correlation of savings rate and future tense marking in languages.

But all this is entirely independent of any genuine causal connections among the traits. For example, if you borrow your writing system from the Chinese, it's likely that you'll borrow some aspects of food culture and architecture as well. This is not because a logographic writing system tends to cause people to use chopsticks or build pagodas.

Keith Chen was also invited to respond to the criticisms and he does so in this post. I found his discussion on the unreliability of the FTR classification rather unconvincing:

Note also, that while typological coarseness may complicate the interpretation of the correlations I find, if anything it strengthens the inference that language and economic behavior are interacting in powerful ways. Why? Well, since these typological distinctions are necessarily noisy, if anything, the correlations we see in data should be an UNDERESTIMATE of the correlations we would find if these characteristics of language could be measured more precisely. To see this, imagine that the EUROTYP FTR classification was effectively no better than a coin flip. Then, we would have expected to find no correlation at all between language and behavior out in the world. More generally, if we think that the classification is by its very nature coarse and messy, then we should also think that if anything, language structure and savings behavior are MORE closely tied than their correlation suggests.