I think the main difficulty in migration from windows XP to linux is leaving word, excel, outlook, ie and powerpoint. If users have already migrated to open alternatives (libre office, ...), the OS switch is almost transparent.
I recently attempted to move everyone in my office to libreoffice where possible and was met with a very large resistence from people who's spreadsheets simply did not work.
it's hard telling people that they have to edit functions/macros that were set up by someone smarter than them 10 years ago.
A UI can be thought of being easy-to-use with the frequency of usage. I have been using Linux for many years. Now, whenever I use Windows the only thought in my mind is how can someone use a software so clumsy.