I consider lightbox functionality to be related to the layout of the content, and hence logically a part of CSS rather than javascript. In CSS3 world, I like to use javascript for the tasks not related to the layout: such as making ajax queries, manipulating user inputted data, etc.
Is there a case for relying on javascript for functionality such as lightbox?
As argued elsewhere, lightbox straddles JS and CSS domains.
I was thinking that in CSS3 world, we should have slightly different breakup of responsibilities (subject to resolving performance issues) - HTML = Content - CSS3 = style/design and changes in style/design - JS = interaction other than purely style/design changes
I see that this breakup may lead to confusion in some situations. (Though I still find it more appealing for lightbox example) So, let me make up my mind when I have more experience with CSS3 :-)