Recently, I had the dubious pleasure of updating a friend's MacBook for OS X 10.6.8 to 10.9. It started as normal, with a backup to DVD of all data that my friend couldn't afford to loose, such as pictures, documents, etc. Normal SOP for significant OS updates.
After that, the update was started. First off, we had to figure out what the Apple ID and password were. That took a bit of time, but we finally found the piece of paper with the critical information. Once we started the update the real fun started. First off, we only had a 500KBS connection. That translates out to an approximately 3 hour download. You get what you pay for, LOL. The reason for doing this update was that my friend needed the speech to text capability that is now part of Maverick. A bit on that later, as all was not what it seems with that application.
So the update downloaded, and the MacBook updated to OS X 10.9, after more post-update updates. Maverick, BTW, has a definition as an adjective of "unorthodox". There were nothing but problems