Mine is yet to arrive, but although I haven't yet had hands-on experience to reply to that part of your question, I have been scouring the web to find out as much as I can about the D600 as I can, both before I placed my order and since while I patiently wait for it to arrive.
I've followed the dust issue and similar issues with other cameras and it hasn't changed my choice one bit. I'm well aware that I have a chance of receiving a D600 that shows dust. But dust is a fact of life. Dust is everywhere, some places more than others. If by some slim chance this turns out to be an endemic issue to this body then it is under warranty for two years, plenty of time to decide whether it's intolerable or not. Those online posters who have found the dust to be problematic enough to return it seem very happy with the replacement. When we're talking about tens of thousands of units it's not surprising something crops up. It's a hassle for those it has been problematic for but otherwise it seems like a tempest in a teapot.
BUT to cut to the chase the reasons that the dust doesn't phase me one bit is because the D600 is exactly the FX digital body I have been waiting for. It is relatively light, packs an ample 24MP sensor, is priced right give or take a few hundred $ and by all accounts has superb IQ - I can't wait.
There's every chance that a D600s MAY surface but that's going to be at least a couple of years down the road if at all. No reason to wait for that, if so you might as well wait for the D500 or whatever other new model will eventually be released. Right now the D4, D800/e and D600 are the state-of-the-art FX Nikons, no better time to buy. Those that say they 'wait for the bugs to be worked out' are simply wasting time. If the body itself isn't up to snuff, replace it under warranty and if it's a firmware issue well then we are at Nikon's mercy - but usually there's at least one firmware upgrade per body and that has no bearing on waiting or not - it's extremely unlikely Nikon would go to the R&D expense to develop a firmware upgrade and not make it available to one and all.
Good luck with your decision - as far as I'm concerned this is IT.... for now...!