I stayed in Edinburgh Backpackers in the summer of 2002 and thought it was pretty decent.
ROOMS: The rooms were spacious and fairly well kept -- all were co-ed. High ceilings and bright colours add to the "character". Unfortunately, so does the climb up the four storeys or so (no lift). Stone stairwell and walls make it a bit echoey. Good beds (not squeaky or saggy) but bad pillows (tiny, lumpy things that may as well not have been there).
FACILITIES: The showers were quite good! I didn't really use the kitchen much, but from what I saw it was a bit crowded.
PEOPLE: The staff were friendly, but unfortunately, because there isn't a great common room, it's hard just to hang out with people.
NEIGHBOURHOOD: The street it's on (Cockburn) is full of funky, fun stores, good nightlife, but the street noise wasn't bad enough to bother me (then again, I always travel with earplugs anyway). I felt quite secure there (if I recall correctly, there was an entry code system). Next door there is a good cafe where you can get a discount when you show your hostel card. Best of all, it's just below High Street and a 5-m downhill walk to the train station (which unfortunately means a *steep* uphill walk when you first arrive by train).
PRICE: When I stayed, it was £14 - this was during Edinburgh Festival time. (Word of advice: *always* book well in advance if you plan to be in Edinburgh during a festival - which is all of August, for example, and at New Year's/Hogmanay).
Overall, a 7.5/10 - pluses: location, location, location; minuses: common areas, some noise