Trello – Some questions about Trello

We don't let you see other people's boards unless they've been explicitly shared with you or made public.

We do let anyone invite you, or you invite anyone, to a board, in the same way you can invite anyone to link to you on a social network like Facebook or LinkedIn.

For instance, you can see me, but not anything about me because we're not in the same organization and don't have any shared boards.

https://trello.com/rich

EDIT

We have posted an FAQ on privacy and security.

https://trello.com/privacy

I agree with your friend about not dividing up into separate boards by type of job.

With your examples such as 'Design ideas' etc, I think they really do fit naturally within different lists on the same Board. It's exactly the sort of usage that Joel demoed in multiple videos about Trello.

The only thing I can think of, to help manage very long lists, is to use Trello's Labels system to put categories on cards, and then use filtering. You should definitely give meaningful names to the default labels.

I wrote up some tips on how to use labels recently.

Having said that, fairly early on the Trello on Trello board got huge, and eventually they reduced the scope of it. So it's does seem to be a well-known problem.