I have some whisperings of OCD. For I don't know how long (since college, I think), any book that I purchase I write my name, the date, the location of purchase, and the price, somewhere inside, near the front.
I've done the same thing with CDs, inside the CD booklet (but curiously, not for DVDs -- or for LPs or cassettes, for that matter).
I have four "running" documents on my computer, where I fairly compulsively log the date, location, price, and misc. notes regarding the item in question: one list for "Music gear" (including guitar magazines); one for computer things; one for woodworking (and gardening) things; and one for sports/exercise/martial arts things.
I keep these lists partly because I'm curious about how much my various hobbies cost me -- and I need to collect the data as it occurs -- because once data is lost, it's gone for good. I also record this information because I'm sentimental, but have a mediocre memory -- so (for example), I want to be able to remember which similar looking backsaw I got from my wife for my birthday; which was from that garage sale down the street; and which was from my grandfather's estate.
And, I'm curious as to how much prices shift over time. So I sometimes browse back through my lists to (for example) see how much a bottle of boiled linseed oil cost me, four years ago.
The upside of my list-making is that I have **very** good records of (some of) my belongings: when we got burglarized shortly after moving to Australia, I was able to give **very** specific details to the cops, and the insurance company, about the guitars that were swiped.
The downside to the list-making is that I often have a backlog of tools (and etc.) piled next to my computer that I'm not "allowed" to use -- because I haven't yet logged them.
I'm OK with that.
Choices, choices, choices.