Due to both laziness, and a lot of my own customization that I don’t want to have to do again, I use variants of a single WordPress theme on all my blogs. And one thing that had been bothering me a little was that individual posts’ pages didn’t show the sidebar.
Today, I finally did something about it, because, after a little thinking, it came to me that it was “hurting” my blogs a lot.
And I don’t mean that in the sense of “not showing the sidebar ads”. It’s a lot worse. The sidebar shows categories, static pages links, links to archives, and other navigation stuff. Someone who arrived at a single post from a search engine, or from the RSS feed, or a link to an article in another site, never saw the sidebar.
Now, it’s true that you can browse to the blog’s front page by clicking on the blog’s title, but it’s not obvious to many people. Including the navigation stuff on every page is very important.
One advantage of having variants of the same theme in every blog is that changing this required just making a diff file after editing the first blog, and using it to patch all the others. 
I had to also change a few ads (the “leaderboard” ones), because they no longer fit on the page.
I just changed this a couple of minutes ago, so it will take some time to see what difference it makes - but I expect a rise in “pages browsed per visit”, and in ad earnings as well.
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Nice change…
IMO, without the sidebar the lines were kind of too long…
With that said, I am a major adept of personal customization. I see blogs as an extension of one’s self… if you’re just using a layout some else made, it’s not your blog. It’s your content, ok, but with someone else’s face. At least, that’s how I see it.
I guess I have to agree.
However, while I didn’t create this theme from scratch, I’ve already made a lot of changes to it (both visible, and under the hood), and it certainly doesn’t look like a blog that just installed and used that theme would.