I enjoy making up cool and unique magic items that have both good and bad attributes. Most of the time, the good outweighs the bad, which makes for a nice, non-generic item for the player that finds it.
When I decided to use Rappan Athuk, I knew I wanted to swap in some of my creations. My party has done a decent job of missing a handful. They almost missed the last one they found. I had to reread to them a "player's note" they had stumbled across 2 weeks earlier real time, but maybe a day game time.
See, I've been running games via G+ Hangouts and (the soon to be no more) Tabletop Forge. It was a pretty decent combination, except that you had to redraw the map with each session and there is no way to give players an actual "handout". What should have been a fair clue was forgotten over the intervening weeks. So, the other week I reminded them of their "handout". They were able to overcome (and then release and run from, foolish party) their adversary, but not before one of the party's thieves found an item I had placed weeks prior.
Strangely enough, it was the one section of the second level that they had bypassed when moving on to the third, before backtracking.
I have no problem letting my creations "rot away" unfound. It's the nature of fate. If they weren't hard to find in the first place, they wouldn't be as memorable ;)
I expect forgotten player's handouts will not be an issue in the future. Last weekend, before the announced merge of TTF into Roll20, I'd already decided to give Roll20 a shot. In part, it was for the mapping with a decent Fog of War, but it was also for the Player's Handouts feature. I expect I'll be giving both features a decent workout in the coming weeks.