Lightboxes, a modal windows, whatever… someone has to stop this.
Like the slider is something that is requested for almost any user interaction
Phones don’t respond well to them
You could end up cropping the window, making impossible to zoom in/out, or worst, the user hit “back” and it could leaving your site.
If you have an image use “open in a new window” link, saves time, css/js and the results are better.
Awful interfaces
I have seen 5 levels of modals, or generate one for things that can be solve with an “confirmation” prompt or even an alert.
Try to use other UI like Tabs, slidedowns, when ever is possible it will be more friendly for the user. Very often the modal is a fast solution because we haven’t spent enough time thinking the right answer to the problem: where to put the form, where add some confirmation button, etc.
In conclusion: modals are the new 90’s Pop Up windows, are related with the annoying advertisement and should be use only if we need to shake the user and screen him “look here idiot, do what I told you”.