I posted a tweet about why I think you should not use dialogs, and it seems people are still pretty skeptical, so I felt the urge to elaborate a bit.
Dialogs invite you to be lazy.
Solving the issue of navigation and interaction within your information architecture of your website or game is a very hard challenge. “Uh, if I just had a good place to put that invitation feature somewhere in my UI..”. If you are a web designer or developer, chances are you shared a similar frustration before. But wait! Thankfully, there’s an easy way out. Just take the feature and pack it in a dialog! That way, we don’t have to clutter our UI and can hide certain features, bring them up when needed. …right?
Let’s turn it the other way around to see what’s going on here. By using a dialog, lightbox or overlay, you are effectively cheating. The content in your dialog will not fit into your centralized user experience, and remains disconnected. Your users have a harder time to relate to features in lightboxes. Even worse, modal dialogs often break one of the most important rules of great user experience: Never block the interaction of your users an your product.
Dialogs are the new popups. So the next time you are setting up a dialog, take a break and think about a better integration.