I find lightboxes for the sake of lightboxes annoying. Sometimes they are useful, when they allow a pop-up interaction to take place without disturbing the page or forcing a complete reload, but more often than not they are just irritating. One that perpetually annoys me is when sites (eg blogs, Facebook and yes, even Sitepoint Forums!) have thumbnail pictures that open up in lightboxes rather than directly into the browser window. This often means squashing the picture to fit the window, which is unhelpful. If the picture loads directly then my browser will compress it to fit the window, but with a single click I can expand it to full-size (which is often necessary to see the detail), but if it loads in a lightbox then that isn't always easy, obvious or even possible.