With the need to hand in a graphic design for my website, I explored several tips of using Photoshop to render website prototyping. Smart object is a very important feature for UI designers. Here are some quick links to some insights of using smart objects.
From Viget-Inspire blog: http://viget.com/inspire/smart-ways-to-use-adobe-photoshops-smart-objects
From Tutsplus: http://psd.tutsplus.com/tutorials/tools-tips/smart-objects/