Here are some examples of titles that I've looked at recently, along with my non-specialist's reactions:
(from Punctum Books)
From University of Michigan Press
If I saw the title alone I would probably mistake it for something it's not. An apocalyptic novel, perhaps. And why is it all caps? The subtitle is very cool though, I'd click to see what it means.
From Digital Culture Books
It's important to understand how title metadata gets used in the real world. Because the title and subtitle get transported in different metadata fields, using a subtitle cedes some control over title presentation to the websites that display it. Four example, Unglue.it's data model has a single title field, so if we get both title and subtitle in a metadata feed, we squash them together in the title field. Unless we don't. Because some of our incoming feeds don't include the subtitle. Different websites do different things. Amazon uses the full title but some sites omit the subtitle until you get to the detail page. So you should have a good reason to use a subtitle as opposed to just putting the words from the subtitle in the title field. DOOM: SCARYDARKFAST is a much better title than DOOM. (The DOOM in the book turns out to be the game DOOM, which I would have guessed from the all-caps if I had ever played DOOM.) And you can't depend on sites preserving your capitalization; Amazon presents several versions of DOOM: SCARYDARKFAST
Another thing to think about is the "marketing funnel". This is the idea that in order to make a sale or to have in impact, your product has to pass through a sequence of hurdles, each step yielding a market that's a fraction of the previous steps. So for ebooks, you have to first get them selected into channels, each of which might be a website. Then a fraction of users searching those websites might see your ebook's title (or cover), for example in a search result. Then a fraction of those users might decide to click on the title, to see a detail page, at which point there had better be an abstract or the potential reader becomes a non-reader.
Having reached a detail page, some fraction of potential readers (or purchase agents) will be enticed to buy or download the ebook. Any "friction" in this process is to be avoided. If you're just trying to sell the ebook, you're done. But if you're interested in impact, you're still not done, because even if a potential reader has downloaded the ebook, there's no impact until the ebook gets used. The title and cover continue to be important because the user is often saving the ebook for later use. If the ebook doesn't open to something interesting and useful, a free ebook will often be discarded or put aside.
Bigger than You's strong title should get it the clicks, but the subtitle doesn't help much at any step of the marketing funnel. "Aesthetics" might help it in searches; it's possible that even the book's author has never ever entered "Decelerationist" as a search term. The book's abstract, not the subtitle, needs to do the heavy lifting of driving purchases or downloads.
The first sentence of "Web Writing" suggest to me that a better title might have been:
"Rebooting how we think about the Internet in higher educationBut check back in a couple months. Once we start looking at the data on usage, we might find that what I've written here is completely wrong, and the Web Writing was the best title of them all!
1. The title of this blog post is the creation of Adrian Short, who seems to have left twitter.