I spent two fall weeks at Cocomama living in the windmill room, a four-person room near the reception desk, and using the common room/kitchen. I kept groceries in the refrigerator, cooked, had laundry done (6€ a load, completed by the next morning), both walked and took the nearby trams, and otherwise experienced much of what Cocomama has to offer in terms of location and services.
The location: Cocomama is excellently situated for guests who want access to the city center without actually staying in the busiest areas. The area felt safe to my 5'2" female self at all times of day and night. There's an ATM around the corner and a large bank across the street, there's a well-stocked chain supermarket a couple blocks away, and several useful tram lines stop in the street outside or around the corner. South a few blocks is the Albert Cuyp street market and inexpensive food options; north is the more upscale Utrechtsestraat shopping and restaurant street that heads toward the center of town. You're also within walking distance of the Heineken Experience "brewery tour" and, further in that direction, the Museumplein, home to the Van Gogh Museum and other major museum attractions. That's a fine walk on a sunny day, too far on a rainy one or if you have mobility issues, but again it's accessible by tram. Finally, I calculated the walk from the red light district to Cocomama to be about 25 minutes on my short legs when I was walking briskly; it was less than 10 when I took a tram.
The hostel: The entrance is deceptively bare, as only the reception desk fits there; doors and winding stairs lead to bedrooms and the common room below. The common room is nicer than I've seen elsewhere, with a mostly functioning TV, oft-used NES, a few DVDs, nice dining tables, two four-burner cooktops, and shared pantry shelves and refrigerator. For the most part, other guests left labeled groceries alone. The spaces were used regularly by guests cooking and eating or chatting in the cushy living room area and playing video games or watching movies, so it was a reliable area to find company for bar or lunch outings. Most evenings there's at least one activity there: inexpensive mixed drinks for purchase, 3€ pasta dinner, or the gathering place before an outing to one of the explicit shows in the red light district.
The rooms: The beds were as excellent as other reviewers say, heavy, wood-framed bunk beds with comfortable mattresses and cozy duvets. Lockers are too small to hold all your stuff, so I ended up using mine for electronics and medications and trusted (accurately) that my roommates wouldn't bother adding my socks to their own travel burdens. Bathrooms are tight but functional, with enough room in the showers for shampoo bottles, a little shelf above the sink, etc--just enough space not to feel cramped. There's not a lot of noise at night unless the folks who live across the backyard are having a party, and closing the window can quiet that; heavy curtains virtually black out the room at night, if that's what you want.
The staff: Friendly, with varying degrees of interest in interacting with guests. Two staff members currently live there, so they're around using the kitchen and working most days; both Elina and Britt were super awesome and welcoming. I also talked a bit with Moo, the only male staff member, who spent many evenings ironing sheets and talking to guests. I didn't interact much with the other folks, though they all seemed nice. Oh, and there's a hostel cat, Joop, who isn't super snuggly but was a good temporary substitute for my own pets.
The guests: When I was there, they were a mix of "this was the first hostel I called that had space" and "I saw how highly rated Cocomama was and didn't need to be in the center of town." Naturally, most were in their 20s, but even among them I think I met about 10 engineers of various types and other interesting professionals in addition to the usual just-out-of-college-and-traveling-for-a-few-months.
So: Cocomama is a hostel, so don't expect perfection, but the convivial vibe and comfortable beds helped me feel at home, and the convenient but removed location gave me access to everything I wanted to experience in Amsterdam. Highly recommended.