I’ve started noting down stuff I wanted about three, four years ago because I got tired of buying the same software two or sometime three times (looking at you, Rage Racer).
My brain somehow gets stuck on the status of certain games, vividly remembering that I wanted them but forgetting to update that the issue had already been resolved last year. So I can’t afford to give it the benefit of the doubt anymore.
If I see a game I want to buy and it’s not on the list, there is a strong chance I might already own it and so I rarely take the risk to buy it. And so far, this has proved rather successful. I think I already escaped four or five new duplicates that I would have swore I didn’t own until I came back home to double-check.
Therefore, it’s not so much a « wishlist » but rather a « safe to buy list ». I use the Notes app on my iPhone, just to make sure I have it on hand whenever it might be useful (browsing through a shop or looking at auctions online).
For digital purchases, I just use the wishlist / favorited feature of the shops.