So as I have said before I have been collecting poser stuff for a long time ( I began in poser 3)  and while I don't have everything I have collected in the computer, I do have enough to get lost from time to time and spend ages trying to locate something not remembering if it is a prop or a character? Clothing is not a problem I have developed a wardrobe system based of the figures. However room, architectures and the list goes on, it can get very confusing. How do you people store your things? if I stored things by vendors would that make it harder or better? 

Here is my list of runtimes.
_installations is used to unzip what I buy online, as I always keep the additional materials with the main character/cloth/Whatever prop.
Same organization for the Zip's/Exe's bought online: always under the name of the item, on my NAS.

In my case, Props keeps everything that's neither landscape-related (thus the  Landscape runtime) nor a human/animal nor a cloth, as they all have dedicated runtimes.
Some are old runtimes that I don't use anymore but keep there just in case.

Special case #1:  Poser 7, which inherits the complete dis-organization provoked by  keeping the original vendors' folders.
Special case #2: Dawn which is naturally nicely organized

When I'm looking for something special, I often use Poser's search function, which could be seriously enhanced, as it's based on a database system. But sometimes, it down not work or the result are too numerous, in those case I use Voidtools' excellent Everything, to search either in the runtimes location or in the original vendors assets

I have things sorted by figure or type. All La Femme stuff goes in La Femme's runtime, morphs, clothing, textures, etc. I put all non-living things into the props folder for any category, regardless of whether they're figures or props. People, animals, aliens, or monsters stay in figures. 

In my other runtimes, I have things sorted by types. Here's my buildings and parts runtime. 

If something is a single prop, it will go loose in the category. If it has multiple pieces, like separate walls or furniture, it gets its own subfolder.

And like Phil's I use the search function or Everything to find things that might not be where I currently thing they should be.

Main Runtime in "Shared", all others under 'External Runtimes' on external drive.