In reply to birdman: Hi Birdman - I have been to Morocco a few times and have used Trekking Hostels.
Last went in 2010 - first time since the kids were born - took my wife and 15 year old daughter, flew from villa in Spain (really cheap flights). My daughter loved the hassle from the Moroccans!
Anyway - try
http://www.hotel-ali.com/ - if you want Central Marrakech, next to Jemaa El Fna, plenty of action then this is fine. Good basic standard trekking hostel. Food okay (breakfast inclusive - not too much) - plenty of evening meals on terrace, accommodation fine.
All I did with the last booking was emailed them (2 weeks beforehand) my arrivals details and turned up. Very well run and close to the Souk, Medina and the Jemma El Fna.
ps - never been in December? Last time it was August and very hot!