CSS3 and JQuery actually make a lot of things simpler. JQuery is full of shorcuts - you no longer have to create exceptions for specific browsers or do stuff like write your own XMPHttpRequest handlers, just use .ajax and you're done. Among other things, CSS3 lets you create design stuff that used to require painful hacks or inline images like rounded corners, shadows, gradients easily.
This guide sums up everything HTML5 -
Dive Into HTML5. One of my clients couldn't believe it when I built a form with (simple) validation with inline dynamic error notifications in a few minutes.
Used to be cross browser compatibility was huge, but now that everyone of them is following standards it's less of an issue, especially now that IE6 is almost dead and IE7 is shrinking by the day.
The most complicated new development in front end work is performance optimization - used to be all you had to do was make sure all your jpgs and gifs were tidy. Since Google prioritizes page speed and users are demanding faster response times from the web, devs now have to make pages stupid fast, tough to do with all the web app rich internet experience crap every site is moving to.
For example one of the top bottlenecks in site performance is browser requests, now you have to do front-end voodoo like packaging and minifying CSS and JS files and deploying images to separate servers. More at Yahoo:
Best Practices for Speeding Up Your Web Site
If you want to do a test project, do it in layers so you learn individual pieces.
Start with an HTML5 layout. Use regular CSS.
Then add a few CSS3 bits to it.
Add a couple of JQuery effects to make it prettier. Like .effect('highlight') when you click on something.
Then add some JQuery that pulls content from a separate page and modifies the current one using Ajax.
Minify your CSS and JS.
Put a bunch of images on the page. Optimize performance on them.
While you're doing this, a couple of tools that will help:
Firefox Firebug Add-On
After you've built your html5 layout and css, right click on anything and click 'inspect element', it will show you everything about it. Edit the CSS of the element in Firebug and you'll see how it effects the layout.
Firefox YSlow for Firebug
Performance stats on your page
CSS3 Gradient Generator
If you're lazy like me this makes gradients for you.
Ultimate CSS Gradient Generator - ColorZilla.com