If anyone is going to Northern Sumatra and you have time, consider a trip down to Bukit Lawang. Even though they suffered that devastating flood of Nov 2003 there is accomodation available and treks into the jungle. Acccomodation can be found at Nora's Homestay (simple clean accomodation 15,000-20,000/night and great food) in the village before Bukit Lawang and also down by the river at places like Bukit Lawang Cottages, and a few other places along from the cottages. Also Jungle Inn much further up is open.
Treks are available and there are plenty of guides needing travellers to come. In my photos I have photographed some guides I believe to be reliable, trustworthy and will have your best interests at heart.
Also I have photographs of my trek as well other places of interest around Bukit Lawang.