No much problems. Watch out for leeches in the jungle. Carry table salt from Mukkali to remove leeches from your legs.Even Mukkali is a remote place, so take care of yourself, avoid being flashy in any term. As far as the forest goes, its safe, unless you dont follow the forest rules.
fees/permits
For Indian citizens, fees are not very high. Approximately, they are in May 2010:Vehicle Jeep rent from Mukkali to the Valley: Rs 650/-Guide charges: Rs 150/-Entry fee: Rs 50/- per headVehicle entry fee: Rs 250/- per jeepCameras still camera: Rs 50/- per camera