I've found DuckDuckGo less good at returning somewhat obscure (but relevant to my search) results than Google. This may be a disadvantage of the "vertical search" approach. I suspect Google's "bubbling" might negatively affect this, but I don't keep Google cookies around long enough to experience it (to my knowledge).
Also the !bang syntax never seemed that useful to me. site: is a much simpler and more useful idea. One thing Google got right was being smart about interpreting the search from the query only, without people having to remember or care about any special options.
On the whole though I do like their approach, and wish them luck.