After installing patch 2.01, I've noticed that corpses clean up, and items in rooms reset after about 3 ingame days, instead of the 30 in previous versions. While this helped reduce the lag slightly, I think the reason lag still exists is because the game does not clean up dropped items. Ever. Arrows that don't hit enemies also count as dropped items, and will also never dissapear, unless they're picked up.

With arrows being fired all the time, the game has to rememver the location/orientation/type of every stray arrow ever fired. With hundreds of arrows fired, this could be the cause of the memory bloat, which leads to LAG.

This could be fixed by deleting dropped items and arrows from the game after 3 ingame days (except in houses you own).