I think that .blog will be successful as a TLD in the sense of significant use, but less clear that they are good domain investments since it seems to me that the main clientele are not going to spend that much for a domain name. Also at standard renewal rates of $23+ it is hard to justify long holding. I see some sense in great words if can get at reasonable prices and try hard to sell them for a year or two then drop if no interest.
One could argue that the TLD is already a success use wise with 185,000 plus registrations only 32% of which are parked and with very decent renew rates.
Bob
(ps I do not, and never have personally had, any .blog domain names although have tracked the parameters on the extension. It is one of those I might get a few of if I see an opportunity.)