Every time there is an official update to WordPress, they also launch a new “official” theme, this time “Twenty Thirteen“. Without exception the CSS and formatting of the new theme breaks the current look of your website in one way or another and you have to go through each and every post and reformat as necessary to make sure it doesn’t look stupid. Alternatively re-code the CSS file to where it’s usable again (which they shouldn’t have changed in the first place!). This annoys the living piss out of me! I can stick with Twenty Eleven (which I will), but potentially miss out on some new functionality, or “upgrade” to the newer theme and go through the hassle of making everything look pretty.
Example of what I’m talking about: In Twenty Eleven H1 looks just like bolded regular text. In Twenty Thirteen H1 is HUUUGE, probably 36 pt. In this “new & improved” theme the images that you so painstakingly have positioned are rattled around. In Twenty Twelve If you have set a featured image it shows by default before the text of the post, but not in Twenty Eleven or Twenty Thirteen.
Otherwise WP is a decent product that is now becoming more complicated and unpredictable than I think it was originally intended to be. 😐