When I develop a website, I always try not to use popups.
There’s something in popups that I don’t like: that they’re popups!
Anyway, sometimes, popups are really useful. So I defined some guidelines that I try to respect when I’ve to use them.
The pages that have to become popup windows shouldn’t be different (structurally or in the layout) from any other page of the website. In fact, since not every user agent supports client side scripting and not every user agent can use windows, it’s always necessary to preview the possibility of browsing the site in a single window.
Users must never get lost with windows. So, when it’s opportune, popups should close themselves automatically.
As soon as possible I will post a real implementation of these guidelines. In the meantime, every comment is welcome.