Everything I have found says the landlord has the right to cash the cheque but that a deposit must be returned within 2 months of the end of the rental. If the deposit is paid in cash then the landlord must supply a receipt. A number of sources pointed out that holding a cheque without cashing would be pointless if the rental was of a longer duration as the cheque would become invalid.
As an aside, if an 'Etat des Lieux' (with full inventory) has not been signed by the tenant at the start of the letting and at the end then the property is deemed to have been left in the same condition as it was found and the landlord has no legal right to deduct damages.
http://vosdroits.service-public.fr/F18391.xhtml
http://droit-finances.commentcamarche.n ... -1-caution
http://fr.answers.yahoo.com/question/in ... 051AAfbnR9