• Open finder
• Select your hard disc
• CommandJ
• Check the top two check boxes (Always open in list view, browse in list view)
• Click use as defaults
• Open Applications->Utilities->Terminal

sudo find / -name ".DS_Store"  -exec rm {} \;

• Enter your root password, press enter

The simplest answer to 'how' rather than 'why' is:

Opt[alt] drag a column sizer. That size becomes the new default, after you relaunch Finder. Only works for column view, not coverflow.

Other options, though each is temporary

• Double click a column sizer to set that column to show full content width.
• Right-click a column sizer for more options.

To relaunch Finder, hold Opt and right-click Finder in the dock. Relaunch will be in the context menu.

Actually there is a simple way to do that.

First you have to open new finder windows (not in Tabs).

Before you click on a new finder window hold the cmd key (not the Option key).

Now you can resize that window or move it around and it will remember that next time you open it.

It is very easy to do this:

1. Open a new Finder window.

2. As you resize the window, hold the Command ⌘ (not Alt / Option) key. Close resized window.

3. Then hold the Alt / Option key as you right click on Finder in the Dock and click Relaunch. Another way to implement this step is to press Command ⌘ + Alt ⌥ / Esc, select Finder from the menu to pop-up and click on Relaunch.

4. Any Finder windows opened after this will open at that size.

Note: This does not work for windows opened from folders on the desktop.

You were clear enough. There is no "autosizing" setting available for the Finder. It's one of the reasons apps like XtraFinder and TotalFinder came into being. I just posted in case you weren't aware of the particular feature. 😎

You can always send Apple feedback of course but "autoresizing" columns is something that has been requested since at least as far back as Snow Leopard.

http://www.apple.com/feedback/

You're welcome.

This is a bug in Mountain Lion for which there seems to be no fix as yet. If you eject the network folder then re-connect it will appear in the sidebar but next time you login it will be gone.