In reply to planetmarshall:
It's worth bearing in mind that this area is suffering at the moment with massive influx of visitors, no doubt driven by the fabulous weather. As such, the police are present at weekends and when the main car park is full (by 10am I would guess) then they are stopping cars from entering. There are a couple of laybys on the Isle of Skye Rd but only for a few cars (<10 overall). I drove past yesterday evening and the red 'Car park full' sign was still on the main road and the car park was heaving although I didn't see any police.
The amount of litter (barbecues, beer cans, etc) is a massive concern too, generally from the local scallies.
The area has very good public transport links and it's worth bearing in mind that the bus from Oldham terminates at the Clarence Inn in Greenfield (also closed at the moment) gives only a 15 minute walk to the main Dovestones car park. Back in the day, I used to run down from the Wimberry boulders to catch the last bus in 20 mins Alternatively, the train from Manchester Piccadilly or Huddersfield stops at the other end of Greenfield which will add c.30 mins on but offers a couple of good pubs on the way back. You are in it for the adventure, aren't you
So make sure you get an early start or take the bus would be my advice. Good luck!
Phil