Rails - Mar 2005 - Best Practices for extracting and reusing code/componants/generators

I know componant is a dirty word to some people around here, but I''d
like to
talk about it. It''s looking like I''m going to start writing a
good bit of
rails code, and I''d like to know what best practices people have
figured out
for extracting portions of an application for resuse.

I''ve noticed a few people have made their own generator for commong
things
like user login control. But wouldn''t that preclude or complicate the 
ability to backport improvements in your login code to older applications?

What about using the new render_componant stuff?

Any thoughts?

jason