It's a small thing but I nearly always forget to check my logo.og.png file post-upgrade and it's often (always?) included in the upgrade only XF zip. It replaces my custom logo image and I don't realize it until I notice it on FB and other sites that use this image.
You can place your logo.og.png somewhere else instead and in ACP > Appearance > Style Properties > Header and Navigation > Facebook Open Graph Logo you can specify the path to this. That way you'll never need to worry about it getting overwritten on upgrade again.