I just upgraded from Mageia 3 to 4 a few moments ago. I installed Mageia 3 last week. Then got the message of mageia 4 on feb 1st.

Although not recommended due to time, I did the update wirelessly. I had no issues at all. It took more than an hour. I didn't pay attention to the time. I did some thngs around the house, did some browsing and deletion of some desktop icons and watched some news feeds while it was upgrading , When it was complete, it told me there are no issues and to reboot my system. No problems at all after reboot.