I recall my tapes sounding ever so slightly worse after each playback. I also once left one too close to my CRT monitor, which erased all the high frequencies from the sound.

Also over time friction would build up in the medium, causing the tape to occasionally resist being pulled so strongly that some sections would stretch and introduce a hard to ignore "wah" effect.

Overall not my favourite means of storing information, like you said - it was fine. I've listened to a huge palette of mixes made by friends for friends and the social aspect of this is something I appreciated greatly.