HTML/5 is it worth learning?
HTML5 isn't an official standard yet, and your millage will vary with what each browser currently supports, so at the moment it's not really imperative to be familiar with it. On the other hand though, it adds some neat new features, and while you can't use many of them right away, in the future it will be the standard so you will have to learn it at some point or another.
It's really not too much to cover or learn, and you can gain familiarity with it as it becomes more prominent. There isn't any harm starting now, and it will probably be beneficial in the long run, but it's not incredibly important for the current time.
It basically just adds advanced form controls, native video and audio tags, the canvas (for drawing graphics), and a few other specialized tags to fit the more modern web. Like I said, it's not too difficult to cover if you already know the surrounding technologies.