When is the_excerpt used in themes?

Forgive this silly question but I could have sworn that the_excerpt was normally used within Category, Date, Month and Year pages.

Has this changed?

Sorry if linking to wp wank offends some but, to be honest, this is where I discovered the issue:

http://wank.wordpress.com/2009/03/
http://wank.wordpress.com/2009/03/11/
http://wank.wordpress.com/category/free-beer-fundamentalists/

I can't even get a page to show the_excerpt anymore.

edit: OK, I can get it to come up on a search:

http://wank.wordpress.com/?s=hands