Curious about text alignment on websites. For a blog, for example, is it better to have left-aligned or justified text? I like the look of justified text but I'm not sure if there's any downsides to it.
There are downsides to fully-justified text. Here's what the W3C had to say in the Techniques and Failures for Web Content Accessibility Guidelines 2.0:
Many people with cognitive disabilities have a great deal of trouble with blocks of text that are justified (aligned to both the left and the right margins). The spaces between words create "rivers of white" running down the page, which can make the text difficult for some people to read. This failure describes situations where this confusing text layout occurs. The best way to avoid this problem is not to create text layout that is fully justified (aligned to both the left and the right margins).
This is especially true if hyphenation is not done properly. I would avoid fully-justified text and stick to left justified in most, if not all situations.
In general, left-aligned text is the way to go. We read from left-to-right (at least in the western world anyway), so anything that strays from this will necessarily decrease readability. Sometimes, using variants can be good - especially when you want to draw attention to something by way of contrast. However, for the most part, you'll probably want to stick with boring, old left-aligned.
There are studies out there that support this, but I don't usually bother with them. Instead, I look at blogs and community forums (like this one or any in the Stack Exchange family) and the most popular sites out there. Try looking at the reviews on Amazon.com, postings to your facebook wall, tweets from your favorite celebrities, and search engine listing results from Google. That's enough to tell me that left-aligned seems to be the way to go. If that's not enough evidence, grab a few books from the best-sellers list or a few dozen magazines and see what they are doing. I'll bet you see a pretty consistent pattern.
Regarding alignment of text you should read this article, it tells a lot :) http://uxmovement.com/content/why-you-should-never-center-align-paragraph-text
IMHO you should use center aligning mainly for menus, tab titles, some cases even for H1 if it suits your site.
I've always found justified text to be overrated. Unless you're very careful, justified text can cause artifacts such as lines with large spaces between words. I suggest that:
The narrower the line width, the less you should consider justified text because the more likely that you are to have artifacts.
The more likely the copy is to updated, the less you should consider justified text because updating the copy will require additional work to make sure your layout doesn't get messed up due to artifacts.