Handbrake shoe linings separating.
They have just gone on my four and a half year old S60 D5. For some time now I have noticed a delayed release from the handbrake.
Last weekend I went to take the car out the garage to wash it, it had been sitting in the garage for a week in gear, handbrake off. The car would not move off as normal, right rear wheel locked solid. Eventually released after dragging for six feet out of the garage.
Contacted Volvo and told not to drive at speed as the now loose lining(s) could catch in the stub axle causing over one thousand pounds damage.
Car booked into local dealer for new set of rear discs, pads and shoes. Cost quoted at just under £400 before VOC discount.
Covered in this thread among others:
http://www.volvoforums.org.uk/showthread.php?t=64804