Unfortunately they're not supported in IE9 or below, which this article oddly fails to mention. So a more accurate title might be "make your UI more responsive for ~60% of your users with HTML5 web workers".
I think this is the case for nearly every technology, new, or old, and although they wouldn't be amiss to mention it, 60% is a lot better than a lot of other techniques which get mentioned here.
Oh, absolutely. Web workers are awesome and hopefully the future, but it seems a bit disingenuous not to mention the huge caveat that currently prevents their being adoptedĀ in a more widespread way.
Sadly, can't even use it for cross-platform packaged apps (min requirement: chromium, iOS browser, android browser) because the android removed support after 2.1.
But if I was working for a chinese market place, or a bank intranet I'm sure it would be 80% IE6.