A few thoughts:
How does the account system work? When I go to log in, I just provide my user information. This means I can only be part of one SlimWiki at a time? This seems like a pretty big limitation for people who might have a company one, one to organize side projects with friends, etc. (For that matter, why is company name required when this could be for side projects with friends just as easily?)
It might be helpful to have an index of all pages (sorted by most recent edit perhaps). I can easily see totally forgetting what pages you have, and while you can search for them, how can you search if you've forgotten what you're searching for?
I can't rename or delete collections, so if I make a typo in the name, I'm stuck with it existing forever. Also for collections, it might be helpful to have a permalink to an index page for the collection instead of just the sidebar. As it stands, you can't link to a collection listing.
Is there anyway to share a page (or provide full read-only access) with someone outside the company?
Somewhat related, I would much rather pay for some service level and be able to add and remove people with various permissions as I see fit (like controlling access to Google Docs) than pay per user per month.
Some day someone is going to ask, so it might as well be me now... is a self-hosted option planned for the future?