You develop a webapp, you have a couple of input fields and buttons on your page. Then the requirement arrives. The customer wants his data to be auto-filled once he enters some identification number (the italian fiscal code). And then, when the data has been filled correctly, he wants the focus to be placed in the 1st empty text box in order to accelerate any further elaboration on that data. Oh ...man!
$("#divPersonData").find("input:text[value='']:visible").first().focus();Setting the focus to the first empty field is really just fun, right?
The essence of this post is that the UI experience gets more and more important in nowadays webapps. Just look around, Twitter, Trello, Gmail,...Think about it if you still live in the somewhat more traditional space of web development.
You might want to take a look at the HTML5