We recently released one of ours into a popular GC that had lots of visitors and after a while of hearing nothing I too started to suspect one of the newbies hadn't realised what it was and had mistaken it for swag, but then we had a few discover logs - from people saying they had seen it but couldn't help it with it's mission, and last week someone finally picked it up and it's traveling with them for a few weeks.
Also, worth mentioning that sometimes TBs in large GCs also fall to the bottom and get mixed up with the swag. We found a large ammo tin over the summer with two Geocoins in there, but they were mixed in with some plastic 'pirate gold'. We took one to move on and placed the other in the clear baggy that held the log and despite having sat undiscovered for a year, someone picked it up the very same week and moved it on.