Off and on, I think about jumping ship to Nikon.
Recently, stores have been offering the D600 with 24-85mm lens at around $2000, cheaper than the retail price of the body alone. It's a good deal if you need a slightly wide to slightly telephoto lens and you're in that hobbyist category they're targeting with the D600.
For me, it would be a way to get my feet wet but I can't imagine what kind of photography I would do with such a combination, since it's rare for me to just photograph, ummm, things.
I was thinking about the 70-200mm f/2.8 lens for sports but in FX/135 format frame mode, it doesn't have much reach. It's fine for the swim meets I'm currently shooting and it would be fair for basketball, although the lack of sharpness at f/2.8 bothers me. If you're working in low light anyway, trying to avoid flash, wouldn't you want your photos sharp? Shouldn't you get a sharp f/2.8 for $2500?
I saw that Adorama had the D800 in a refurbished state for roughly $2300 with a 90 day warranty. That's about $700 off but you should buy an extended warranty to avoid problems since Nikon don't have 1 year of confidence for you. (What's with the U.S.A. only warranty anyway? If I travel and have a problem, I'm out of luck?)
The D800 is solidly above the D600 in a similar way that the D300s has been above the D7000. It's a weighty decision, literally. The extra functionality comes with a great deal of extra weight and size. The D800 is no F2 but it's bigger than the D600. I'm all for smaller gear, and many professionals have been working with mirror-less cameras lately.
Also, one of the review highlights I've noticed is about the D600's suitability for sports. DPReview mentioned that the auto focus wasn't really good for sports. I don't really depend on AF much and when I do, it's a single focus point. I really don't care whether I have 51 auto focus points if they only work under certain conditions with certain equipment. I'll get AF lock on my target and move back to my intended composition. (No, I don't just point at something and hold the shutter release and hope that I get a good photo.)
Picking up a refurbished D800 for $2300 + 3 year warranty for another $300 + a 70-200mm f/2.8 for $2500 + tax seems absurd at this point, unless I'm charging too much for photos. "Excuse me, I'm selling these 4x6 shots for $25.00 each. How many would you like?" "Well, no, I'm not retiring to an island in the south Pacific. I'm just paying for my equipment to photograph your son."
Hey, maybe I could find a refurbished 70-200mm!