I can't say how strongly I disagree with the first reviewer!
I,too,have read both books and there is actually very little crossover between them. Poulson's book is basically a story that takes place on the west coast of America, whereas Glenny ranges from there to Turkey via Ukraine,Britain,Germany and elsewhere.
I do agree on one thing, that for those interested in the technology, Poulsen's is a more detailed book (albeit a little too detailed for me). But for those who want to know how cybercrime actually relates to ordinary peoples' lives and about the psychology of hackers and criminals on the web , I would say Dark Market wins out for sure.
As regards the specific case of DarkMarket ,which I followed in 'Wired' magazine, both bring what looks to me like real inside knowledge but much of Glenny's stuff has never really been written about before (at least I've never come across it before)- for example about how international law enforcement agencies do or don't co-operate, plus I found the stuff about Germany and Turkey really eye-opening.
But most of all, I couldn't put it down- I read it in two sessions because I couldn't help myself.