The Weary Traveler, Tulum
This hostel has the best communal set-up, and hence the best communal atmosphere, of anywhere I've stayed so far. The central courtyard, which dominates the place, houses a long row of tables, a few hammocks, a deluxe (and used-by-all) kitchen, and a bar. I met some great people here, and felt that I could really unwind as well.
Rooms: average, no complaints.
People: really nice and friendly, if a bit hippie-inclined.
Staff: friendly, English-speaking, and good-looking.
Location: main street of Tulum.
Food: significantly above average — free eggs, pancakes, sausage, etc. for breakfast.
Internet: free, but never available (numerous good cafés nearby).