Will items dropped on the ground ever disappear?
With the Thieves Guild missions to steal X worth of items from Y, I find myself with a lot of useless items that aren't even worth selling.
So usually I just stop and drop everything on the ground. Unfortunately, this means that Riften now has random piles of plates and goblets and other random garbage everywhere. I guess they don't have sanitation workers in Skyrim.
Will these items eventually disappear or will I have to do a special thief "mission" to steal all the garbage off the ground and dump it in a container?
Eventually yes, it will disappear. Every once in a while a city resets. A (usually, and it worked for me) way to do this is to make a new character and then load the old one. This will cause the entire world loot to reset so if you have some bodies laying around they will disappear and if you have stored some things in an unsafe location it too will probably disappear.
Throw the items that you don't want in a spot that you know you wont go.
Cell reset is affected by visiting it, so if they are somewhere you often pass trough, they may never disappear. So letting them laying in a city where you have a house is counter-productive.
Yes they do disappear after a while. I would suggest buying a house and storing your items in chests or storage spaces.
Items dropped in the ground, like weapons and shields (even by NPCs); Ghostly Remains, Ice Piles, and Wisp Cores are currently not cleaned up at all (they remain indefinitely, contributing to save game bloating and game lag).
In the PC, this is fixed by the Unofficial Skyrim Patch:
Ghostly Remains, Ice Piles and Wisp Cores will no longer permanently remain and bloat the save file (they will either disappear on exit of the cell or when the cell resets).
NPCs will no longer drop weapons or shields as separate objects, as these are never cleaned up which greatly adds to save bloating and litters the gameworld (the items will still appear to be dropped, but will access the corpse's inventory to be taken and be cleaned up with the corpse if left)
Ash Piles used to remain indefinitely (was not properly cleaned up by the game), but has been fixed since official patch version 1.4. Nirnroot lighting or glow objects also used to be not properly cleaned up by the game, but has been fixed since official patch version 1.6. Related official patch changelogs:
Fixed issue with ash piles not cleaning up properly
Fixed issue with nirnroot lighting not properly cleaning up