How to automatically count amount of cards? In some list, or in the board.
Click on show menu on the right side of the board if its not visible.
From the Menu option select Search Cards.
In the text box type
* to "filter by everything".
All cards will remain visible and you'll also get card counts at the top of each list.
If you use Chrome, there is an extension called CardCounter
It does the job but i'm looking for something nicer.
I am using this extension for Chrome: CardCounter For Trello.
This extension shows me the total cards that I have in my board.
All you have to do is keep the filter "*" on.