These are serious bugs and worth being noted again.

1. Ash piles stay in the world forever.
2. Weapons and arrows enemies drop and shoot stay in the world forever, the weapons tend to float in air after a while as well.
3. I think that when enemies drop their weapons and its not swept from the world on the outside of ruins, the enemies never respawn.

These three things have have been within a stretch of one year game time.

4. The exploding items bug that makes decorating your home impossible.
5. The Blood on the Ice quest I cannot even begin.
6. Save game bug, when your saves trail off screen they fade away but they are still there. Example I save from 600 to 620, I can only see save 610 and up, then I delete some extra save save 601 randomly disappears I delete some more it reappears. Also if you try to save over say save 610 it saves over save 615 instead. This is bothersome with multiple characters.

Adding to this, it looks like the arrows from a 'bound bow' also remain forever too. i.e. if you miss the target you are aiming at, and the arrow lands on the ground, they stick there forever. I tried this by firing an arrow from a 'bound bow' into the ground in Whiterun. It never got cleaned up after waiting, or travelling to other locations and returning to Whiterun.

Regarding the weapons floating in the air, I think this may be a problem with objects in general. For example, when outdoors and running across the landscape, I frequently see objects like animal skulls floating several feet above the ground. If I nudge them, they move and drop to the ground. The problem seems to be associated with the initialization of the object when it first appears (i.e. when you first enter a room, or when it comes into range when outdoors). Maybe this is also realted to the problem of dead bodies appearing halfway in the ground. This is most obvious when you do the Companion quest to (i think) fetch a piece of the axe, and you return to Jorrvaskr only to find it has been attacked by the silverhand. When you first approach Jorrvask and you see Aela standing near a couple of dead 'silver-hand' enemies, the dead silver hand enemies always seem to appear halfway in the floor. You find that either their head and chest is in the floor, or their legs are in the floor. Reloading to a previous save before you enter Whiterun and then returning to Jorrvaskr, you will find they are in a different position. It is almost like the position and orientation of their bodies are being reset to garbage values. If the developers are reading this, please check that all of your variables that specify the position and orientation of newly created objects are being reset, otherwise they could be using values of whatever garbage was in that memory location previously.

I am wondering if this is related to the object bug mentioned above. If an objects position is initialized incorrectly and it begins partially within a wall or other object, then the Havok engine will attempt to resolve the collision by pushing the colliding object(s) apart. This can cause them fly apart when you first enter a room. Assuming these problems are related, hopefully fixing the initialization problem will prevent the 'objects exploding' problem that makes homes so messy.

Xbox 360 Bug Report Topic v2 can be found http://www.gamesas.com/topic/1326952-xbox-360-bug-report-topic-v2/