I have 2007 Cooper S with leatherette and the quality is better than the cloth seats for sure.
The leatherette seats do not come with lumbar adjustment as in upgraded upholstery seating from half leather and up.
The cushion of leatherette is not as soft as lounge leather (haven't tried sport seat full leather).
However, I would opt for leatherette again b/c it looks really good and hard to tell if it is real leather or not to casual eyes. In addition, spending extra $1500 to 2000 on a few feet of leather does not have as much impact as opting for a premium package or Aero Kit.