Cool Stuff - Friend of Foe?

As you are able to add additional capabilities to your forms, make sure that you aren't doing it at a cost to accessibility or usability. The pattern attribute is a great example. There are a number of great sites out there that can help you specify specific input (one of my favorites is http://www.html5pattern.com/), but if you are going to put constraints on what people can enter, make sure to give VERY specific instructions. Labels help a lot too.

Placeholders are a nice way to provide suggestions, but don't forget that they disappear as soon as they come into focus.

For now, just play with everything you can and add as much to your forms as you can. But when the time comes, make sure you are using these skills for good, not evil.