When I first joined SL in 2006, I never organized my inventory. I learned that that was a very poor decision.
When I created my new account, I organized everything on the first day. I add/move/alter a folder whenever need be, but otherwise, my inventory is kept very neat - as soon as I get a new item, I put it where it belongs so I do not have to deal with it later. The result is an organized, uncluttered inventory where I know where everything is, when I need it.