Edito
Designers seem to like using modal windows more and more, as they provide a quick way to show data without reloading the entire page. It's easy to use and easy to design.
The big problem I experienced with every plugin I tried either using Prototype/Scriptaculous or jQuery is the customization. They say you can do whatever you want simply but that's not fully true. The default CSS works fine, but most of time it's a mix between r[......]
