Most web sites that I see are centered, and I’m wondering if there’s some sort of unwritten (or written) trend away or against left aligned sites?
I don’t have current statistics, but studies done by Smashing Magazine in 2008 and 2009 found that 94% of popular blogs and 89% of design portfolios were center-aligned. It’s a small sampling of websites, of course, but it indicates that the overwhelming trend is toward center-aligned websites.
If I had to venture a guess, I would say that the reason for this is because of increasingly bigger monitor sizes. Most web designs simply don’t look good on 20-23-inch monitors unless they are centered.