Right now Knack has page level permissions with the login pages. This is great but I think similar functionality needs to extend to views. Here's why....
I design my detail pages with the parent record on top, and all its connected child records in tables below. This is pretty much the standard way of displaying parent-child relationships in a database. Suppose I have an object called "customers" which stores all your clients basic contact information. Customers has a child object called "Accounts" which might have billing data associated with that customer. When displaying a customer record, you want the billing dept. to be able to see the account info below, but hide that from everybody else. There's currently no way I see to do this. This means you have to create separate customer detail pages with different child records displayed for all permission types. This is duplicating the work and grows incredibly complex given multiple permission levels and multiple child objects.
You could fix this by simply adding a "Permissions" field to the view options, and hiding any view that the logged in user doesn't have access to.