I've had my d800 for four months and have used it about ten times as much as I expected. My plan was to use it in place of medium format—not because I think it's "as good," but because the technical camera kit I'd like to have is orders of magnitude out of my price range.
I've been pleased with the big camera style work that I've done, although I find working with the dslr to be a bit fussy and clunky compared with working with 4x5 film (where most of my experience is).
The big surprise is how much I've taken to using it as a small camera. I got seduced by its nimbleness and low light abilities immediately, and it suckered me into starting a project that seems almost like (gasp!) street photography. Not my usual thing, but there it is, and inspired by a stupid camera!
I'd be harder pressed to say I've fallen in love with it, though. I'm finding it to be a very trustworthy and capable tool, but there's something about the software and all the little buttons that keeps it from really feeling like an extension of my nervous system. I don't know if this is the cameras fault, or if it's just me being a luddite ... most of my photo experience is with cameras that have big knobs, no batteries, and the basic technology of a wind-up clock.