All Lightbox clones that I have tested have issues with keyboard accessibility, making it unnecessarily difficult or confusing to use them without a mouse.
WAI-ARIA, the Accessible Rich Internet Applications Suite, helps developers make their web applications more accessible to people who rely on assistive technology. Start reading up on it.
To save keystrokes and speed up development I have created a DOMAssistant bundle for TextMate.
When using getElementById to get a reference to an element via the id attribute, IE may return an element whose name attribute contains the value you’re matching.