Nautilus's thumbnail cache in
~/.thumbnails has grown to several hundred megabytes.
Do I need to be concerned about unrestricted growth of this in the long term, or is its size automatically managed somehow?
Thumbnail cache is limited to 512MB, so several hundred megabytes sounds logical. It also shouldn't keep files older then 180 days.
If you want to change it, try
Exactly the same solution is aplicable to 12.04. You may need to install
For 14.04 you need to install
It's size is automatically managed, because it has a built in limit of 512MB by default, and deletes thumbnails older than 180days. It will not cache files above a certain size limit either:
If you want to manage its settings, you can use Ubuntu-Tweak (See how to install it here: How do I install Ubuntu-Tweak?):
As it is mentioned in an above answer, for 14.04 dconf editor from dconf-tools should be used. However, I only found the key under