For example, when posting to a blog via email, the user can enter [tags x,y,z] to add tags via email. How "technical" does that feel to the average user?
You can't expect that users know before what is a shortcode. If you never used email you don't know what cc and bcc is, but you will figure out. Shortcodes are not like a button that stands there: "click me to see what is happening".
First of all, every plugin or theme developer choose the name of the shortcode. You have to read the description of that plugin to know what shortcode to use.
If the user already know how to install a plugin, read its description to see what is the name of the shortcode then he knows how to use them. If not, he will not know but it is very easy to just say: "to do this you have to post [thisshortcode], to do this other thing just post [theothershortcode]". Anyway you have to contact them to tell the name of the shortcode you used even if they know what a shortcode is.
From personal experience, we have a wordpress blog for a range of people* to contribute blog posts to.
* Mainly developers, technical people, and a handful of managers.
We have shortcodes to embed vimeo and a few other things, and the answer to your Q from my experience:
No. They need training on how to use shortcodes. We have a wiki on how to create posts, which has a section on how to use the shortcodes.