This plugin was born out of the need to use the label-over-field method for forms that I was working on. There are other plugins out there that do pretty much the same thing, but none of them had the - for lack of a better word - sexiness that I was looking for. I'm also obviously fully aware of the HTML5 placeholder attribute, but again, while it's a step in the right direction, it's just a bit too static for my liking (and not compatible in older browsers).
My implementation of this method makes the label slide across the field (by default - can be turned off) when gaining focus and fade out when a value is entered. If you want to see a kind of demo of how it works, check out my 'get in touch' page which uses a version I'm working on that has a tooltip feature rolled in as well.
You can find out more and download it by going to it's home on github.
As always, feel free to comment and let me know if you find any bugs!