I see the code for them in the template file ("begin tabs" in block_product_details.html, right?), but they don't appear on the front-end. Is there a setting I have to change in the control panel to make these appear?

I'd like to know the answer to this as well, thanks :)

Please check CMS settings for product details block for product details page.

Thanks for the reply :) However, I'm not sure the tabs are in that area.
 
In block_product_details.html on line 247 begins a section called Begin Tabs, and it appears that there are some features that are available within tabbed content. Nothing in the CMS block settings refers to tabs.
 
Is this perhaps a feature that is no longer available, or is it just not available yet, or is it there but I'm overlooking it?
 
Thanks :)