YES, Horrible IQ and really really slow focusing! Nikon doesn't have teleconverters for that lens 3rd party maybe but IMO not even worth it if you were to find one.
I disagree. The results obtained from using a teleconverter depend on both the TC itself, the lens to which it is attached, and the camera that both are attached to. While it is very true that many (perhaps "Most" perhaps only "Some") TC's do indeed cause horrible image quality that statement does not hold true in every instance.
Using a 2x TC on a long lens in an effort to double an already long focal length seldom works well. Using an inferior TC makes the situation worse. I have a 2x TC that I consider to be inferior and I will not use it on anything at all. In fact the results from using it are so poor that I won't even sell it because I don't want to stick someone with it. On the other hand I have a 1.4x TC that I've used on every lens I have (including the Nikkor 70-300) with excellent results most of the time. In poor light conditions or in when it causes me to have to use a low shutter speed it does not, but as long as there is plenty of light it works very well.
TC's cause a corresponding loss of light. A 2x TC costs 2 EV or 2 full stops of exposure, and will turn a f/4.5-5.6 lens into an f/9-11 lens. A 1.4x TC costs 1.4 EV.
With many lenses that loss of light puts the lens into a range in which most camera bodies will not autofocus since many camera bodies require a lens of f/5.6 or wider for the autofocus unit to work. My D7000 has not had any significant problems autofocusing, even with my 150-500 lens and a 1.4x TC.