No issue with crop sensors themselves, but do have an issue with resultant holes in the lens line-up available for crop bodies, with some manufacturers showing a major reluctance to fell gaps that exist in their crop sensor line-up that do not exist in their full frame sensor line-up.
I suppose there are swings and roundabouts, but do find the lack of certain lenses a problem. For example a 50mm makes a nice 75mm-equivalent lens for my Nikon D300, but on the flipside there is no real option for a nice 85mm/ 105mm equivalent on dx designed specifically for portraiture.
I suppose as mentioned, a full frame body and a crop sensor body would be the best of both worlds. I do know I would love to be able one day to use Nikons portrait lenses as they were intended, particularly the very nice defocus control ones (105mm and 135mm), as on crop sensor DX bodies, they are far too long for me. Same with their 85mm f1.4 lens, which becomes a headshot/ outdoor only portrait lens for me.