Transition Steps – Making the Old New Again!
Old Create Content Screen _layouts/15/create.aspx
Good Series from FBWeb on SharePoint 2013 Upgrades
http://blog.fpweb.net/series/sharepoint-2013-upgrades-in-a-nutshell/
What's New
http://technet.microsoft.com/en-us/library/cc303422.aspx
What's Gone
http://technet.microsoft.com/en-us/library/ff607742%28v=office.15%29.aspx#section1
Office Issues – Office 2010 and 2013 products on same PC
http://sharepoint-community.net/profiles/blogs/sp2013-problem-office-2010-and-an-office-2013-product-on-same
What Might Not Work
http://en.share-gate.com/blog/not-working-after-sharepoint-migration-to-2013