Right, I know I've asked about this in the past, but I tried searching the forum to no avail.

Which containers in Jorrvaskr are safe? Particularly those downstairs, in and around the Harbinger's quarters; currently, I'm using Jorrvaskr for my PC's home, and it would be nice to sort my things out, instead of cram everything into the one end table with the daedra heart on it. According to the UESP, dressers and wardrobes are also safe, but I know that is supposed to vary from place to place.

Does anyone know for sure?

Looks like only after being Harbinger..

Put something in worth one gold.. fur shoes or something and then wait.. 30 days in game I think..

See if it disappears.

http://www.uesp.net/wiki/Skyrim_talk:Jorrvaskr#Safe_Containers.3F

When you go downstairs you end up facing the room where there is a bed you can use. If you proceed straight from the entrance to the door of that room you will be directly facing a set of drawers. I've been storing things in there since the beginning of my game and my stuff is still there. It appears safe and is close to the entrance and a bed.

Well, I sorted out all my stuff into all the containers in the Harbinger's bedroom, as well as the end table with the daedra heart on it. I waited 31 or 32 in-game days (just to be sure), checked all the containers--and lo and behold, everything was there.

30 days is the cut off for indoor container respawning, yes? If so, all the containers in the Harbinger's quarters are hereby discovered to be safe

Did you stay out of Jorrvaskr for the full 30 days? Not even one visit?

I think the 30 days have to pass without interruption or the timer resets.

Ah, I didn't leave at all--I'll reload the save and test it out later.

So, even in a respawning container, if you re-enter the cell, the timer will reset? That might make the whole thing moot anyway, as I know I rarely ever go 30 days without at least a single trip back to any home I'm using, Jorrvaskr included. But, worth a test, anyway!

Yes, I believe that's how it works. I know what you mean about visiting so frequently that it doesn't matter. I used Fort Dawnguard for storage during one playthrough and thought it was safe. However, the real reason my stuff didn't disappear was that I was in there constantly. I used the same storage container during the current play through and my stuff disappeared after 10 days.

Sometimes, it's easy to drift away from your base without realizing how much time has passed, be careful!

Kami12 is correct: each time you enter a cell you reset the timer. It's been that way since Morrowind, if not earlier.