I'm familiar with the way html & css work together. Recently I was previewing some html5 content demo'd by apple and saw they used a html5/css/javascript. I'm at the point where I need to know whether or not javascript is a must-learn; or if I can find similar workarounds with CSS3 & HTML5.
Edited to clarify intentions:
My aim is to have a roll-your-own blog page with twitter feed and some basic animations.
Do I need to learn javascript?
Yes, you should learn Javascript.
No, you don't have to learn Javascript.
The long version:
Javascript is only needed if you want your page to do something. If the page is static it's not needed. Some things may not be very interesting without it though (<audio>, <video>, and <canvas> come to mind).
More specifically in response to your question, Apple's examples are probably not static (I'm guessing a lot of them are related to the three tags I mentioned before), so if you want to do things like that, you need to learn Javascript.
You will, almost always, find that you want to do something that either HTML5 or CSS3 will not let you do. JavaScript is not "hard" to learn if you understand basic programming and if you don't it's a good place to start.
Development is all about adding things to your toolbox. If you have HTML5 and CSS3 and have a good understanding of JS, you'll be more valuable to customers than if you only know HTML5 and CSS3. For browser based development, JavaScript (and it's libraries) are invaluable.
My aim is to have a roll-your-own blog page with twitter feed and some basic animations.
Yes. Learn the basics of JavaScript, then look into jQuery.
Depends on what kind of page you're developing. Most new sites are very dynamic and its users expect a desktop like performance and UI, in which case you WILL need javascript (sites such as facebook, gmail, portals, stackoverflow...)
Looking forward to where websites and user experiences are going, learning Javascript seems like a 'must-learn' to me. As I have learned more about web-design, I have also begun to see the wisdom in separating content (HTML), from style (CSS), from actions/interactivity (JS). Although I don't personally use it, I know a great place to quickly get going in Javascript is using jQuery. Personally, I use the YUI library from Yahoo because I found the support their site provides (examples, API docs, and videos) easier to learn from. Another gem from YUI is their YUI theater which are great talks about YUI and general javascript development. I hope that helps!